In Internet Explorer 10 (possibly earlier versions as well), when content is displayed in an overlay the admin toolbars obstruct the top portion of that overlay. In some cases that obstructs key components such as tabs and icons.
Here's a screen shot of a properly positioned overlay in Chrome:
http://jrp3.net/warehouse/Overlay_Chrome.jpg
And here's a screen shot of a not-so-properly positioned overlay in IE:
IE: http://jrp3.net/warehouse/Overlay_IE.jpg