I have observed this issue in Test complete version - 11.0 while scripting, when trying to undo the script changes suddenly TC got exit, I was shocked. Recently TC 11.0 was upgraded to TC 11.2 issue is observed in this version also.
I feel like it's a defect. Can i report to TC development team?
I just tried what you suggested in TC 184.108.40.206 and was unable to reproduce the issue. CTRL-Z only undoes the changes.
I would agree with Michaud. It sounds like, for some reason, the CTRL-Z keybinding has been improperly associated with closing the application. You can try and reset the defaults in TC or do the uninstall/reinstall to reset them.