Nice! Ran that immediately and it works perfectly. Seems _keyhit indeed lacks the issue in _keydown; I still don't have my mind around how _keyhit is supposed to capture multiple keys pressed at the same time, but that's the first code I've seen in which the issue vanished. I'll have to do some messing around and testing to educate myself on how _keyhit works under various circumstances.
This did have a good side-effect, too. In experimenting with other default keybinding setups, I found that Lctrl-Z-X-C is in fact a bit more comfortable than Lctrl-Lshift-Z-X. In the latter, whenever hitting shift, I realized I felt a bit like my ring finger was having to reach over my pinky finger a bit. Which is not good, as Lctrl+Lshift is the combination that would produce a blink-teleport.
Thanks for the help.