I don't know if combound xbows have to worry about this or not, but I use a Horton Legacy (recurve) and I need to make sure that the center serving is aligned correctly when cocked. If I don't have the same amount of serving coming out of both sides of the cocking mechanism, my bolts can move from side to side (opposite side of where the center serving is longest). I think what happens is there is more torque on one side of the bow and it forces the arrow in the opposite direction when released. As far as dropping, I don't see that unless the broadhead is not in line with the spine of the bolt (such as a bent tip or bent blade, or just off-center to begin with).

I would agree with GrumpyTom, if the bolts are impacting randomly, something is amiss with the balance of the bolt. Check the broadheads for true alignment or more subtly, possibly a loose blade in the broadhead.

Cheers!
MadOtis