I noticed a problem in the Two-Weapon Rend feat and searching the Paizo forum, I found my own post about this.... posted in August 2008!!
Reference -> [Bug] Two-Weapon Rend feat
I checked the FAQ and found no mention/correction.
So, HOW is this feat handled if (for whatever reasons) you suddenly have a strength below 10!?
As written, Two Weapon Rend incorperates 1.5 your Strength Mod whether positive or negative. If it only calculated a positive mod, then the feat would say bonus, if it only wanted negative, then it would say penalty
I don't see a bug.