In general anything relatied to horse/cart and or "Rotation" of character/horse - can be fixed, for now, with slipcor's save fixer
You can find it on the game-page from the link text "All here" near the mention for slipcor there - and one of the last two/most recent versions should work for your situation.
( also just in case - http://mlbs.slipcor.net/ )
also be wary - as the Horse in general is still one of the buggiest parts of the game, and will likely be so for a few updates until more important aspects are hammered in and ironed out.
If you, for example, ride the cart - You may end up with player rotation being off and/or player sheet being inacessible - both can be fixed with the same save fixer program, and in general, both (the player rotation and horse freakout/rotation/etc) are caused by the horse