Hi John...
I understand this issue well. I think what's happening is that the model is actually regenerating but the pattern instances are failing. The little red "stop light" at the bottom of the window is supposed to alert you to the fact that there are failures. You should see a small box at the bottom which pops ujp in the event of a pattern failure. the box should warn you that some features failed to regenerate. Is this not happening for you?
Thanks!
-Brian