When you are editing a subscreen, you go to add something, and select "(None)"
ZQuest crashes 😞
((from the Screen/Room editor)Quest->Misc Data->Subscreens->
(any subscreen)(mine was "active subscreen (triforce)"😉->Edit->Edit->New->
(select "None"😉=CRASH!)
Subscreen editor bug
This doesn't happen in 536.