My CSS editor doesn’t show the same line numbers as you, so I remmed out all “position:relative;” references between the /* Menu */ and /* Menu bugfix */ lines. This solved the problem, though a little quirky. I ended up putting each one back in until I found that the problem is solved by only remming the one at my line 425, which can be seen here:
Line 425 /* position:relative; */
Line 426 float:left;display:block;width:100%;
Again, the problem is solved, but it isn’t the optimal solution.