Does this happen only when you have a project loaded, or at all times? Does it happen only when TestComplete has keyboard focus? Can you speculate on recent changes that caused this issue to "suddenly" appear?
Easy thing to try is to uninstall/reinstall TestComplete to see if that makes a difference. Uninstalling may unregister any stray hotkeys that got associated with TestComplete...
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 188.8.131.52 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.