Drag and Drop Items Locking After Dropping

One of our team members ran into an issue in a Drag and Drop question with multiple draggable items. Whenever multiple items are dropped onto the Drop Target, one of them becomes locked and can no longer be dragged. It doesn't seem to be a layer order issue or something that can be fixed by messing with the Drag and Drop options.  Any idea why this is and how we can fix this? Thank you!