I see what you mean.
When hovering on a cat. that has subcats. then the image becomes slightly bigger in the bottom and displaces the rest of the menu down.
Please note that this doesn't happen with FF, only occurrences are with IE6 and 7.
The answer is that FF is a much more standards-compliant browser.
I am not embarrased to admit that I don't know of a fix for IE, it is a goofy browser, this error happens in my site too.
On the bright side, it is barely noticeable, I wouldn't worry about it.
Better eliminate that blank image in your menu, instructions are in this same thread, just look back a few pages.
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