Horse have the ability to glitch themselves through fences and apparently through walls. Ive seen them get through my fences easily because they are very determined to get where they want to go.
A workaround is to not use fences but countless wide fence doors. Those can be locked and will keep horses in/out. They cant get through those. But thats not really a solution.
Ive been seeing my horses constantly outside their fence but didnt see them leaving. Only once I saw a horse navigate itself through a fence by walking backwards and turning. Just now I saw horses inside another fenced area and Im sure I locked the fence door for horses. One of the horses left on its own, the other followed a few seconds later. The horse walked right through the door. I locked the door for horses again... and the horse turns around and just walks right back through the door inside the fenced area...
I call the horse to its sleeping place but the horse couldnt leave the fenced area. Because the door is locked for horses.
*facepalms*
