[UDN] Anim Notifiers in animation sequences don't trigger if the end-user drags it all the way to the left

Under certain conditions, dragging an anim notify to the left in the editor makes it unplayable

UDN case :

[Link Removed]

• Open an Anim Sequence
• Drag to the right, so the start of the sequence stays around the middle of the track
• Add a new Anim Notify anywhere (for example a sound, so you can hear it when it triggers)
• Drag the Anim notify to the start of the sequence, but moving the mouse more to the left of the start of the sequence
• Play the sequence
• Result : The sound does not trigger