Short description of error
The cornerpin node in Blenders compositor can't render with motionblur, making it unusable.
Exact steps for others to reproduce the error
Just cornerpin somthing, move it around, render it and be sad that there is no motionblur.
The Plane Track Deform has an option for Motionblur, but in some cases it is just overkill to setup a track first. IMHO the two nodes should actually be merged into one...