@ haiddasalami : yeah, but maya applies the value to the upper and lower bend, so you get a full circle by entering pi. @ Mark : no, it's just a nice interface that replaces the paint effects one. The problem is still there.
For this object I wouldn't bother using a motion path. A bend deformer will do the job in a cleaner way. Go to the animate menu, then do Create Deformers > Nonlinear > Bend. In the bend curvature field, enter 3.142 (this field is in radians, not degrees, so you need to enter the value of Pi for a full circle). You'll…