[SOLVED] Page Menu items disappear when window is re-sized in IE

Is this a bug? It's making me nuts. If I resize the browser using the "restore down" button (middle one of the top right buttons in IE) and then maximize the window again.. the page menu disappears. refresh the page and it reappears. this does not happen in Firefox, only IE. I've been picking away at this for hours and nothing seems to fix it. Here's the client's test site : http://www.unityhamilton.com/unity2010/ .. I'd be grateful for any thoughts, I'm tearing my hair out here. (site is made in Atahualpa 3.5.3 WP 3.0.1)