Happens to me consistently, on this browser.
1) Go to any thread where there are a few posts by users with a Folding postbit (and example given below).
2) Open one of the postbits.
3) Now, try and open someone else's.
You'll notice that all that happens is the first one closes.
I would like to see either:
1) The new one opening, and the first one remain open (this is my preference, since it allows you to compare two people on the fly).
2) The first one closes and the second one opens.
Only tested on IE9.