Sometimes your eye can be confused by the fletching on the arrow as it spins, making it look like the tail end is spiralling downrange.

If the tail end is actually spiralling, then you've got fishtailing and porpoising going on at the same time. Might be you had small tuning misadjustments that the 4" vanes were hiding, but the short Blazers can't compensate for. (?)

Another thing...You sure you're not getting rest contact?