http://www.cerb4.com/forums/showthread.php?t=2444
Someone in the forums discovered this and was able to narrow it down to the description you see. I have verified that particular case and done some auxiliary testing and it appears it is only broken as described.
From a purely Q/A standpoint this one is tough to test in a comprehensive fashion, but I'll keep playing with it and report any additional details or related issues.
I think the issue is that the message refresh obliterates the 'first reply' ID on the <DIV>. jQuery could handle this much better -- should be fixed in a couple mins.