Fixed at revision 27115.

The problem was only in the app itself, not in the component. A change related to ICE-7540 had modified the width of all menus, including the menu bar, so another CSS rule was added to restore the width to 100% to the menu bar.

Tested fix with code revision 27120 in IE9, IE8, IE7, Firefox3.6.
Re-opening because of the following issues:
In IE9, the menuBar renders now vertically (all pages), and according to description on the page it must be horizontally oriented.(IE9.png attached)
In IE8, the menuBar is not style correctly (IE8.png attached).

I just re-tested this fix with revision 27120 and the problem is already solved. Note that the fix is in the showcase code itself, not in ACE. So, to test it, the showcase app has to be rebuilt and re-deployed. Also, make sure you correctly clear the browser's cache. This problem actually affected all browsers, because there was a CSS rule explicitly setting a narrow width to all menus.

Re-tested with revision 27126, in IE8 & IE9.
Issue is fixed indeed, I had to clear the IE browser cache a few times to see the menuBar displayed horizontally.