Menu display bug

I'm using an instance of FCKe in a Yahoo UI dialog. This dialog is a movable div width dynamic size.
The problem is that when I open a menu (font size, font family, etc), the menu don't appears on good place. In fact, it is decalled by the position of the YUI dialog :
if my dialog is at 100x100, the menu will be at 100x100 from its normal emplacement.
When I display full screen mode of FCKe, menu appear normaly.

Could you fix this bug please ?

Thanks.