Fixed!
With a little help from a friend, I managed to fix the acorns in the left-hand menu! It turns out that IE gets thoroughly confused occasionally and needs some elements specified in the CSS down to the nth degree before it will work properly. Sadly, I haven’t been able to replicate the same trick on the right-hand menu so I’ve done a little hacking around so that the right-hand menu has no acorns. Poor, deprived menu.
The acorns are still there in all other sensible browsers, though.
That trick also doesn’t work with the blog post titles, so they’re still being hacked around to work dully in IE and work in full, maple-leaf glory in Firefox, Opera etc.
One day, Microsoft will release a browser that actually does the same things that other browsers do and we’ll be able to junk all the hacks. Until that day, we just have to find new ways to work with the ‘undocumented features’.