Not all bugs are IE’s, and Chimera’s CSS implementation isn’t always perfect. Every CSS spec I read says:
An element’s padding is the amount of space between the border and the content of the element.
So setting padding:10px; should not cause the border of a box to move – it should cause the contained content to be pushed in, as with the padding attribute for table cells. But no… Chimera pushes the DIV boundary out instead, forking up the design. This is solvable by creating a new containing class and applying the padding on that. Not elegant, but seems to work in all CSS browsers.
Update: As far as I can tell, this is the official bug report on the issue. Scanning through the comments is an object lesson in just how difficult it can be for browser makers to interpret the W3C’s recommendations. The Mozilla team really cares, but even with the requisite will-power, some ambiguities are difficult to resolve. Kind of like Biblical or Constitutional interpretation — except that in this case the framers are still alive ;)