When cantering, my mare pauses mid stride, as though she is going to do a flying lead change (yes, she knows how to do these), and then goes right back into the same lead she was on. This is also compounded by the fact that she whips her head up in the air.
I've been having people more experienced than I ride her, including a trainer (who unfortunately lives out of state, so he doesn't get up here often). Out of about 4? People (again, more experienced than myself) I've had ride her, she does the afore-mentioned "special moves" for half of them. The most experienced riders she doesn't do it. Wondering if less-experienced (who don't know how to cue the flying lead change, and don't own horses who do this) accidentally give her a partial cue to do a lead change, but don't follow through? My mare tends to bop her head furiously when she is confused, so this is the only thing that makes sense. The trainer had her doing beautiful flying lead changes and cantering very nicely: he did mention she fell kind of hard on the forehand and once she was cantering, she kind of balked and slowing, but proper conditioning would help her (as might a harsher bit).
I detailed the situation a little more in the English Riding forum, if you are interested. Please help - I'd love ideas, and even more, I'd love to hear stories of horses who may have done this and it was corrected!