I recently switched to the "new" theme on Debian's wiki. I realized
there is now an overlap between the 2 first top horizontal bars. The
first bar contains for anonymous a "Login" link. The second bar contains
"FrontPage", "FindPage" and "HelpContents" by default. When the cursor
hovers the second bar, the tab hovered becomes highlighted. The problem
is the area highlighted goes up to the top of the page, so there is
overlap with the first top bar (at least for the first tab). This
problem didn't exist with the classic theme.
This happens both in Iceweasel 10 and in Chromium (testing).
This problem doesn't happen with the classic theme. Note that switching
themes currently takes an unreasonable time. I also had an error once.