Frostbite with frost bolt TBC

[Gregoriano]

When casting frost bolt rank 1 I got frostbites atleast 12% of the time, but after casting 110 frost bolts rank 13 I havent seen it proc even once, was testing on mobs.

[Mayhem8]

Something is definitely fishy. Frostbite seems to affect rank1 just fine, but I got no procs out of rank13 and managed to get a low proc% off rank12. I'm not sure, but it might be affected by other talents in the frost tree. Bad nerf to frost anyhow qq.