I dunno if it will still occur in the new version
But for version .82
Use Slipcor's Save fixer - the last version or one just before it (should say either player or horse something something)
The issue is replicated by physics and orientation due to the Carriage - Riding in the cart "perfectly" may not be noticeable after dismount
But when the cart freaks out even slightly, hits a bump, or freaks out alot, the screenshot you provided occurs very easily.
There's also times when you're so off-base, you're practically swimming (gliding) across/inside the ground
And the engine just isn't setup to answer that (yet)
Save fixer will absolutely fix it