diff --git a/src/elements/SwpEventElement.ts b/src/elements/SwpEventElement.ts
index 1ea565e..003d6e5 100644
--- a/src/elements/SwpEventElement.ts
+++ b/src/elements/SwpEventElement.ts
@@ -250,6 +250,7 @@ export class SwpAllDayEventElement extends BaseEventElement {
     const endDateStr = this.event.end.toISOString().split('T')[0];
     this.element.dataset.start = `${startDateStr}T00:00:00`;
     this.element.dataset.end = `${endDateStr}T23:59:59`;
+    this.element.dataset.allday = 'true';
   }
 
   /**
diff --git a/src/managers/AllDayManager.ts b/src/managers/AllDayManager.ts
index 143b8b1..806782b 100644
--- a/src/managers/AllDayManager.ts
+++ b/src/managers/AllDayManager.ts
@@ -367,7 +367,7 @@ export class AllDayManager {
 
     // 2. Normalize clone ID
     dragEndEvent.draggedClone.dataset.eventId = dragEndEvent.draggedClone.dataset.eventId?.replace('clone-', '');
-
+    dragEndEvent.originalElement.dataset.eventId += '_';
 
     // 3. Create temporary array with existing events + the dropped event
     let eventId = dragEndEvent.draggedClone.dataset.eventId;
@@ -390,7 +390,10 @@ export class AllDayManager {
     };
 
     // Use current events + dropped event for calculation
-    const tempEvents = [...this.currentAllDayEvents, droppedEvent].except(dragEndEvent.originalElement);
+    const tempEvents = [
+      ...this.currentAllDayEvents.filter(event => event.id !== eventId),
+      droppedEvent
+    ];
 
     // 4. Calculate new layouts for ALL events
     this.newLayouts = this.calculateAllDayEventsLayout(tempEvents, this.currentWeekDates);