When you put platform behaviour and drag and drop behaviour on the same object then you
suspend the object in the air it starts to slip.
Maybe it's supposed to work with the grvity
Ta-daa...
<img src="http://xs130.xs.to/xs130/08342/gravity839.png">
I didn't notice any "slipping" but when I released the platform sprite it would instantly fall at maximum velocity. This fixed it, and theoretically should take care of your slipping issue too.
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thanks deadeye