kivy/kivy — pull request #1657 by matham (2013-11-30 04:39:08+00:00)
Title: Don't allow negative sizes.

You should not be able to have negative size, right?

Currently, the size of the children will be negative if the layout's size is zero with non-zero padding. But that screws up the way the children are presented.

But even if negative size is acceptable, in this case a user would not want a negative size, only zero.