New horse problems

Sounds to me that he's clearly in some kind of discomfort, or emotional distress (ie, is anticipating the "pain" to arrive)... I would eliminate things like lillie suggested (chiro, teeth, saddle fit) first. I also completely agree with JDI, some horses dislike the nutcracker action and work better in a double jointed it. My gelding is currently in a Korsteel Oval Mouth Eggbutt Snaffle (my god it has a longgggg name lol) and I wouldn't put him in another bit again... he loves it.

i have a horse who really cant stand a jointed bit, but goes happily in a loose ring straight bar- which looks big and chunky, but is actually one of the kindest bits.

Sorry for the late update. Computors been down. Anyway, yes I did have him fully checked over, top to bottem, prior to purchasing him. Everythings 100%. Also, the saddle fits fine.
I did end up putting him in a stage 1 Myler comfort snaffle and it has almost completely alleviated the inverting. He's breaking at the pole and giving to the bit. We still have some problems with walking through it a little bit, but instead of upgrading to a more severe bit or getting a curb we are starting to practice working of body position.

He seems to be a MUCH happier, more relaxed little guy these days. :)

"loose ring straight bar- which looks big and chunky, but is actually one of the kindest bits."

FYI its not that kind if it has no bend. joint absorb some of the pressure on the edges of the mouth. If a bit is big and chunky it might even be too big for a horses mouth. My mare cant use most thicker bits, her mouth is just too small.