This is version 2.5.1. Line 53, it reads
mDrag.onDragFinished = OnDragFinished;
Should that perhaps be
mDrag.onDragFinished += OnDragFinished;
so it doesn't stomp any event handler the user might have attached directly to the draggable panel?
Might need to check first and make sure the delegate doesn't already contain the functionality to avoid multiple calls. I'm not really clear on what happens there if you try to add the same function to a delegate, and I couldn't find a definitive answer.