Post: #7

56b is too outdated and have many bugs like this, so the most recommended solution is update your sphere version

but if you don't want to, maybe this can be fixed using scripts too but it will require some weird workarounds. Everytime a player ride an mount, the mount NPC will become "invisible" (disconnected) and will change current ACTION to 111 (ridden). The correct behavior is always stay at ACTION=111, but as I said, 56b have some bugs and for some unknown reason it was changing this value, making the worldsave detect this NPC as an "mount not acting as mount". So to prevent this problem, you must make sure that the ridden NPC always have ACTION=111

I don't recommend and don't know how you can do an workaround like this, but it's the only way to fix this problem if you don't want update your sphere build