Well, I tried doing Replace instead of Replace all, and it doesn't repro when I step thru each replace operation one at a time.
But now, I've gotten into a case where the Find dialog won't open.
I type Ctrl+H, the buffer looses focus, but no find window.
Alt+Space usually is good for finding lost windows, but it doesn't help here.
Restarting Slickedit didn't help either.
Hm... retrying Ctrl+H many times and it finally comes back.