I found some bugs wile messing around in custom battle:
You can place infinite kings of any color.
Rolling logs can't be placed.
All ground traps can be infinitely overlapped.
those aren't bugs....you might have to be in king vs king mode for you not to spawn a million kings (as it says when you click on the king thing to place one down that it will act as a normal unit without king vs king)
the rolling logs can be placed,you just have to click in the right spot
the ground traps are like units and I'm pretty sure you can stack units tooso really none of these are bugs.