There is a bug in IE... My headache has been lasting months over this!!! Anyways... to save you all the grief...
For the following CSS file
\Portals\_default\default.css
Add the following lines:
div { display: inline-block; }
div { display: block; }
No more disappearing content. I can't tell you how many times I have had issues with content disappearing. It could have been when I was rolling over links... or child DIV elements..., but this saved me.