no, i dont see the problem visible there.. i think what happens is: the bones normal orient is ZERO
-when i look down, it changes to a negative(or positive,not sure)
-when looking up, it changes to a positive

the only things i see in the model editor is that the bone flips its rotation when positive and flips back when going negative, and in-game, this affects the attached weapons...
-oh and good job with preva, maybe if ur working on a sequel i can add some ideas