This is funny because it's not really a bug at all. I side with the PHP guys on this one. Passing in a string to a number_format function is not even proper form in the first place. I do agree that it should always default to 0 instead of null because it is a numeric function, but still. The usage is the main problem in this case - and who wants to fix a bug for an asshole anyways?

A lesson to all who rely on edge cases and un-documented behaviors for functionality.