PPro CS4 locks up when clip reversed

Question

We're using PPro CS4 on 64-bit Vista machine.  We have several clips that had a dust spot in them, so we created a mask to cover the spot.  PPro worked fine after doing this.  Our problem occurs in one clip that we want to reverse (we want the clouds to move the opposite direction).  PPro locks up.  We've tried reversing the clip, then creating the mask.  We've also tried creating the mask, then reversing the clip, either way PPro locks up.  What are we doing wrong?  Below are the steps we use to create the mask and reverse the clip.
1.  Clip is on the timeline in Track 1.
2.  Right click on clip, Speed/Duration, Reverse Speed
3.  Render clip to ensure playback is what we want
4.  Right click on clip, copy and paste to Track 2
5.  in Track 2, apply Gaussian Blur to blur out dust spot
6.  Create a new Title, using the Ellipse Tool, cover spot
7.  Title Properties, ensure color is completely white, close Title screen.
8.  Drag created Title to Track 3 and adjust clip duration to equal Track 1 & 2
9.  In Track 2, apply Track Matte Key and in Matte option choose track 3.---this is the point that PPro locks up.

Answer 1

Thank you!!!  We tried your work-around and it worked perfectly.  We really appreciate your advice.  It's also nice to know it wasn't something we did wrong, but in fact is a bug.