This seems only impact IE7. Have tried IE8, FireFox 3.6 and Safari 5 (on Windows) - all look fine.

Some Crucible drop-down menus or links (such as "Tools", "Complete", "Reopen", "Join Review", etc) appear on top of the history drop-down menu. The similar UI elements in other applications don't have this problem.

This doesn't seem to be related to the new header, as it exists with the old header as well.