diff --git a/src/app/_helpers/collections/difference.spec.ts b/src/app/_helpers/collections/difference.spec.ts
new file mode 100644
index 00000000..ea9fab3d
--- /dev/null
+++ b/src/app/_helpers/collections/difference.spec.ts
@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2022 StApps
+ *  This program is free software: you can redistribute it and/or modify it
+ *  under the terms of the GNU General Public License as published by the Free
+ *  Software Foundation, version 3.
+ *
+ *  This program is distributed in the hope that it will be useful, but WITHOUT
+ *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ *  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ *  more details.
+ *
+ *  You should have received a copy of the GNU General Public License along with
+ *  this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import {differenceBy} from './difference';
+
+describe('differenceBy', function () {
+  it('should return the difference of two arrays', function () {
+    const a = [1, 2, 3, 4, 5];
+    const b = [1, 2, 3];
+
+    expect(differenceBy(a, b, it => it)).toEqual([4, 5]);
+  });
+});
diff --git a/src/app/_helpers/collections/difference.ts b/src/app/_helpers/collections/difference.ts
new file mode 100644
index 00000000..dc012234
--- /dev/null
+++ b/src/app/_helpers/collections/difference.ts
@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2022 StApps
+ *  This program is free software: you can redistribute it and/or modify it
+ *  under the terms of the GNU General Public License as published by the Free
+ *  Software Foundation, version 3.
+ *
+ *  This program is distributed in the hope that it will be useful, but WITHOUT
+ *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ *  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ *  more details.
+ *
+ *  You should have received a copy of the GNU General Public License along with
+ *  this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/**
+ * Returns the difference between two arrays.
+ */
+export function differenceBy<T>(
+  a: T[],
+  b: T[],
+  transform: (item: T) => unknown,
+) {
+  const disallowed = new Set(b.map(transform));
+
+  return a.filter(item => !disallowed.has(transform(item)));
+}
diff --git a/src/app/_helpers/collections/group-by.ts b/src/app/_helpers/collections/group-by.ts
index 688ae807..b17ccc0b 100644
--- a/src/app/_helpers/collections/group-by.ts
+++ b/src/app/_helpers/collections/group-by.ts
@@ -21,7 +21,7 @@ export function groupBy<T>(
   group: (item: T) => string | undefined,
 ): Record<string, T[]> {
   return collection.reduce((accumulator: Record<string, T[]>, item) => {
-    const key = group(item) || '';
+    const key = group(item) ?? '';
     accumulator[key] = accumulator[key] ?? [];
     accumulator[key].push(item);
     return accumulator;
diff --git a/src/app/_helpers/collections/uniq.spec.ts b/src/app/_helpers/collections/uniq.spec.ts
new file mode 100644
index 00000000..ca8e4a56
--- /dev/null
+++ b/src/app/_helpers/collections/uniq.spec.ts
@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2022 StApps
+ *  This program is free software: you can redistribute it and/or modify it
+ *  under the terms of the GNU General Public License as published by the Free
+ *  Software Foundation, version 3.
+ *
+ *  This program is distributed in the hope that it will be useful, but WITHOUT
+ *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ *  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ *  more details.
+ *
+ *  You should have received a copy of the GNU General Public License along with
+ *  this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import {uniqBy} from './uniq';
+
+describe('uniq', function () {
+  it('should return an array with unique values', function () {
+    const array = [
+      1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
+    ];
+    const result = uniqBy(array, it => it);
+    expect(result).toEqual([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
+  });
+});
diff --git a/src/app/_helpers/collections/uniq.ts b/src/app/_helpers/collections/uniq.ts
new file mode 100644
index 00000000..4d88d258
--- /dev/null
+++ b/src/app/_helpers/collections/uniq.ts
@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2022 StApps
+ *  This program is free software: you can redistribute it and/or modify it
+ *  under the terms of the GNU General Public License as published by the Free
+ *  Software Foundation, version 3.
+ *
+ *  This program is distributed in the hope that it will be useful, but WITHOUT
+ *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ *  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ *  more details.
+ *
+ *  You should have received a copy of the GNU General Public License along with
+ *  this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/**
+ * Filter out duplicates from an array.
+ */
+export function uniqBy<T>(
+  array: T[],
+  transform: (item: T) => string | number,
+): T[] {
+  return Object.values(
+    array.reduce((accumulator, current) => {
+      accumulator[transform(current)] = current;
+      return accumulator;
+    }, {} as Record<string | number, T>),
+  );
+}
diff --git a/src/app/modules/data/chips/add-event-popover.component.ts b/src/app/modules/data/chips/add-event-popover.component.ts
index acb45177..cce63201 100644
--- a/src/app/modules/data/chips/add-event-popover.component.ts
+++ b/src/app/modules/data/chips/add-event-popover.component.ts
@@ -35,6 +35,8 @@ import {ThingTranslatePipe} from '../../../translation/thing-translate.pipe';
 import {groupBy, groupByProperty} from '../../../_helpers/collections/group-by';
 import {mapValues} from '../../../_helpers/collections/map-values';
 import {stringSortBy} from '../../../_helpers/collections/string-sort';
+import {uniqBy} from '../../../_helpers/collections/uniq';
+import {differenceBy} from '../../../_helpers/collections/difference';
 
 enum Selection {
   ON = 2,
@@ -267,13 +269,16 @@ export class AddEventPopoverComponent implements OnInit, OnDestroy {
   async onCommit(save: boolean) {
     if (save) {
       const {selected, unselected} = this.getSelection();
-      console.log(selected, unselected);
-      this.scheduleProvider.partialEvents$.next([
-        ...new Set([
-          ...this.partialDateSeries.filter(it => !unselected.includes(it)),
-          ...selected,
-        ]),
-      ]);
+
+      this.scheduleProvider.partialEvents$.next(
+        uniqBy(
+          [
+            ...differenceBy(this.partialDateSeries, unselected, it => it.uid),
+            ...selected,
+          ],
+          it => it.uid,
+        ),
+      );
     }
 
     await this.popoverController.dismiss();
diff --git a/src/app/modules/schedule/page/grid/schedule-day.component.ts b/src/app/modules/schedule/page/grid/schedule-day.component.ts
index f4c0d190..50830880 100644
--- a/src/app/modules/schedule/page/grid/schedule-day.component.ts
+++ b/src/app/modules/schedule/page/grid/schedule-day.component.ts
@@ -1,16 +1,16 @@
 /*
- * Copyright (C) 2021 StApps
- * This program is free software: you can redistribute it and/or modify it
- * under the terms of the GNU General Public License as published by the Free
- * Software Foundation, version 3.
+ * Copyright (C) 2022 StApps
+ *  This program is free software: you can redistribute it and/or modify it
+ *  under the terms of the GNU General Public License as published by the Free
+ *  Software Foundation, version 3.
  *
- * This program is distributed in the hope that it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
- * more details.
+ *  This program is distributed in the hope that it will be useful, but WITHOUT
+ *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ *  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ *  more details.
  *
- * You should have received a copy of the GNU General Public License along with
- * this program. If not, see <https://www.gnu.org/licenses/>.
+ *  You should have received a copy of the GNU General Public License along with
+ *  this program. If not, see <https://www.gnu.org/licenses/>.
  */
 import {Component, Input} from '@angular/core';
 import moment from 'moment';
@@ -40,7 +40,10 @@ export class ScheduleDayComponent {
   dateSeriesGroups?: ScheduleEvent[][];
 
   @Input() set dateSeries(value: Record<string, ScheduleEvent>) {
-    if (!value) return;
+    if (!value) {
+      delete this.dateSeriesGroups;
+      return;
+    }
 
     this.dateSeriesGroups = groupRangeOverlaps(
       Object.values(value),