I think I found what creates the error.
The object has a CoronaLightMtl where "Emit Light" is unchecked.
If I give the object a CoronaMTL and sets the self illumination multiplayer to 1 and add the texture to that channel, the motion blur renders correct.
Makes sense?
I will not upload a file here in public, but i will open a support ticket so this problem can be looked in to.
OK?
Stephen