It is indeed a bizarre bug.

It happens 90% of the time on my home machine using IE. It happens under 5% of my time on my office machine running IE. If I use Netscape 6 on my home machine it never happens. If I use Netscape 6 on my office machine it always happens.

This is all completely reproducable...

Both machines have been through the IE5 -> IE5.5 -> IE6 upgrades, none of which changed their behaviour.

A very odd bug. I have resorted to using only IE6 on my office machine and only Netscape 6 on my home machine for reading the BBS.