It always happens to me, and I've never found out why. When I have 4 frames and all standard (on Revision2 subscreen) Current Items, Roc's Feather, and 1 text on screen on my subscreen editor, doing simple things such as rotating the cursor (with all the numbers correctly set) or viewing properties causes it to crash and/or freeze. Once I exited the editor with the subscreen like that, and when I returened to the editor I selected to edit that subscreen and it crashed. I don't know if it's just me, but it's been happening for a while. I do NOT use the NOT IMPLEMENTED items, so let's get that out of the way now, too.
Subscreen Crash
Unfortunately the subscreen is buggy as all hell, has been for some time :-/
Please just keep reporting the bugs as they come up, and the more specific you are about what you were doing at the time of the crash, the better.
The (a?) bug that could crash ZQuest when viewing object properties is fixed in the next beta.