AdamT
Indeed. Pasting references (or dragging nodes) into Wrangler snippet boxes, then ctrl-z undo will sometimes clear the contents of your script - the menu Redo doesn't see the action, though Alt-R with your cursor active in the snippet box will *sometimes* restore the previous state. When it doesn't, well, I go outside and look at the sky for a few minutes
Re expressions not registering, I usually find simply ctrl-shift-LMB to delete the channel clears it up (though it can happen again of course!).
I just wanted to say that I hit this and have been pulling my hair out for hours trying to figure out how to get the field back. Even creating the same node from scratch in my PointVOP did not fix it. All of them were coming in like this. The Alt+R did the trick.