Facebook mutual friend problem?

Hi..So Im checking on a person's facebook, however I do not have them added as a friend. I checked their mutual friends number on their profile which had said she has 4 mutual friends of mine. However, when I checked it only listed 3. Is there a bug or is that 1 friend missing from the 4 friends hiding their friend things?

2012-08-11T18:06:21Z

are the 3 friends that I see , are only our 3 mutual friends? when i clicked to see our mutual friends, the number says 3. but on the overview of her profile it says 4.

?2012-08-11T17:52:13Z

probs just a bug