For example: When the computer's date changes, and a smart collection "capture date in the last X days" contains e.g. 50 photos before midnight, and 40 after midnight on the new day, the smart collection as such works correctly, i.e. selecting something else and then the smart collection again will show only the 40 photos that match the rules *now* - and the film strip info shows correctly "... / 40 photos". However, the number of photos indicated to the right of the name of the smart collection still shows "50". The only thing that seems to refresh this number is to restart lightroom.
This is of course not a severe bug, but it may be irritating sometimes.
P.S. Seen on LR 3.4.1 on WinXP 32 Bit SP3.
P.S. I have seen some other occasions (not date changes) when the number of photos to the right of the smart collection's name was not updated when something was changed for the photos. However, I was not able to pinpoint the exact circumstances. Normally, this number is updated correctly.