Well, kinda, but it looks different in different browsers (as you say)
so it's hard to tell what you consider a bug!
Depending on how you look at it, either you should do a major
restructuring of the markup or just do a spot fix. I don't like the
current styling so much, because you end up with weird dependencies
where (for example) *increasing* the left margin on #menuBox element
lets it flow to a *wider* width because it bumps it around some
floated stuff.
Anyway, one way to look at this is you simply overflowed your 960
grid. <ARTICLE> has 850px to give. #subNav is 340, #menuBar is 514px.
That's 854px. Lower #menuBar to 540px and, at least in Webkit, it no
longer wraps.
-- S.