Just for the record:The original Debian bug report is more than a year old and it was an issue at *that* time (see http://www.w3.org/TR/2005/WD-CSS21-20050613/visudet.html#abs-non-replaced-width). The relevant paragraphs got changed in the meantime (Nov 2006) and there should be some rationale behind it...
So, now it seems to be a bug in the gecko engine :) Cheers, Jens