This is in b16c. When I accidentally edited a screen, I tried to undo my mistake with "U". It didn't work. Undo in the menu is clickable, but it doesn't do anything. It could be my laptop's keyboard, but it might not, so I'll put it here as a bug.
Undo bug
... Confirmed. o.o' The only where an "Undo" doesn't work here, I think, is when placing a combo down though. Undoing things in the Tiles and Combo pages works just fine.
This bug is still in (142)
Confirmed.
I think this is fixed, but make sure...