What is going on with the druid spell Animal Growth??

[joenic2]

So my bear tank with 9 druid levels casts Animal growth and I get 1:39 duration. I hover over the spell on toolbar and sometimes it says 1:39 but sometimes it says 2:15. I thought it was a visual bug but no, it gives me 2:15 when cast. Then sometimes 1:39 again. It seems random and I don't know why it is doing that. Just a moment ago it even said 3 mins but when cast it was 2:15. The wiki says that the spell is based on this :9 seconds / caster level. I am level 9 druid so nothing I can think of should be randomly changing the duration. The math is even wrong. I should get 1:35 and not 1:39. I don't have extend feat either. Anyone else getting this weird thing? I am trying everything to recreate why it would switch and nothing seems to be the problem other than randomness.

[kpak01]

So my bear tank with 9 druid levels casts Animal growth and I get 1:39 duration. I hover over the spell on toolbar and sometimes it says 1:39 but sometimes it says 2:15.

Is it only Animal Growth? How about some other random spell, like Resist Energy, does it go from 9 minutes to 13 minutes? If so, the question isn't, what's going on with Animal Growth, it's, what's going on with your caster level?