if you have the latest version of the menu (1.3.0.6) then open up the spmenu.js file and find the line
this.delaySubmenuLoad=(spm_getAttr(o, 'delaySubmenuLoad', '0') != '0' && spm_needsSubMenuDelay());
and change it to
this.delaySubmenuLoad=true
I believe this will be a configurable property in the next dnn release. It already is in my menu.
Bear in mind that this setting will make the submenus wait to render until the page is completely loaded. And in case you wondering, my menu is
the only one suffering from this IE bug.