ChangeMaster to MasterTitle Slide After CloneSlide results in corrupt PPT that blows up Powerpoint

Part of my application merges slides from a repository into a central presentation and changes their masters to a common master. Then it removes the unused masters.

In the case of title slides, I call changemaster and pass the master title slide as the master.

This has worked well, until the attached case. One very odd thing is that I can reproduce this case 100% of the time, and 100% of the time, I can change the second slide cloned into the master presentation in the same way and it will all work ok. If I simply delete 4 specific shapes, it works perfectly. Any other shapes make no difference. The shapes I delete have all the same properties (except position and actual text) than the other 8 similar shapes on the slide.

Please take a look and let me know. Any help is greatly appreciated.

Phil