Add Backdrop Problem

I've come across a problem when using the "add backdrop" action.

Here is a quick example:
http://download124.mediafire.com/gmm9wmzdbhpg/mm5ygy45azn/Example.mfa

I want to get rid of the "trail" effect...

Basically, when the frame is scrolling, the "delete all created backdrops in layer 1" action ceases to function and a trail of backdrops is left behind until the frame is still again.

Has anyone else come across this problem and/or found a solution to this? Any suggestions will be gladly appreciated!