If you filter (using upper right box) something (for example filter out 1 specific person), this works for all selected contact lists.
However, if you are switching between a specific contact list (not 'All') and 'All', the list is not refreshed. The result of the last selected specific contact list remains on screen.
Confirmed to exist using:
* 1.8.2 release
* nightly 23-12-2011
* nightly 07-01-2012
P.s. This bug was first mentioned by me (on the wrong place) on Sun Dec 25, 2011 16:05; I posted a first bug report, where I promptly received a response. I should check if it still existed in the nightly build. Sadly it is