Resizing exists.
The window is still feels itself as maximized. It cannot be moved or resized but can be restored/maximized by window buttons. After restoring and maximizing it maximizes correctly. Upper gap is from previous window of Firefox. Every time appears a new button in taskbar with
Microsoft Excel title which activates last worked excel workbook and disappears.

This bug is not regular and appears once-and forever after many of desktop switches and when more then one of excel worksheets are opened and are not active when swithicng desktop. After once appears are observed every time desktop switching. And even can be observed when Excel window is not maximized. Upper gap is a part of
previous desktop and is detected by mouse cursor as window border.

I think it associated with not-standard view of Excel window title.
System XP, "classic" view of windows, Office 2007 SP2. On Word, PowerPoint and other Office applications not observed, only with
Excel.