The fix is implemented in _AddNewCOS function.Its not best solution, but works for me.
When the player have 1 horse summoned and summon 2nd horse, he must use teleport before summon 3rd horse.The query will delete all previous registered horses in DB _CharCOS and when the player use teleport again,only last horse will stay summoned.
!!! Create backup before use this.And check the ID of horses in your db before proceed !!!
This is the code:
Save the function after modification,you don't need to restart the game server.More RefObjID can be added like ID's of mall transport .
Regards