Total aggression factor too high

My total aggression factor is shown as 11.00 I'm playing a very passive game lately, because I don't wan't to lose quickly. Many aggressive players have smaller AF than me, I don't really get it. I check and check and never bet. This could be a bug, I don't trust this number at least - I play on poker stars. And I have played more than 300 hands. But it's only my own AF that seems to be too high. I think I can trust what pokertracker writes about the others.

