That explains that then. I was about to post exactly the same thing thinking it was a bug. I'll go back and try that puzzle again to see if I can get it in six.
However, when you do try and solve the puzzle with that layout, the REJECTED screen tells you the reason you failed is because you haven't given each bug the correct amount of space each (which isn't true), not because you've used too many boxes. That's probably why there's some confusion.