If you modify the start position for the wipe, you can adjust the interpolation for the transition.
To adjust a preset SMPTE wipe:
(a) Alignment box (b) Duration field (c) SMPTE Pattern Number field (d) Global Axis box
If you scrub the transition, you should see the wipe make a large jump at the last frame.
The jump in the wipe should be gone and the interpolation for the wipe should be fairly even.