I'm running a website at http://www.tuc.org/ which is using the DynaMenu module of Post-Nuke (which of course wraps this code) for menuing. The horizontal menu at the top of the screen is causing problems on IE for some users, and I suspect it's the PHP Layers, not DynaMenu, at fault. The problem is that sometimes all of the top-level menu items overlap each other in the middle. Moving the mouse over them will sometimes spread them back out again.
This doesn't normally happen to me when browsing the site, but I've found that it can be replicated by changing the text size, e.g. from "medium" to "larger" under IE's View menu.
It could very well be that something in Post-Nuke, or something in our site-specific style sheets, is causing the problem, but I have no idea where to start looking. Any suggestions very welcome!
Finally tracked this down, posting the answer in case others have the same problem. Turns out that it was because the top-level menu items were embedded in a narrow DIV. No idea why Firefox handled this properly, or why IE would let them break out of the DIV by moving the mouse over them.
Many apologies for casting doubts on PHP Layers. Mea culpa!