No the 'double mount' isnt fixed with that system.rar you posted :
iv had a mount before cm patch 1.50
no duplication
iv had a mount before cm patch 1.60 beta
the mount is being cloned no matter what you do, even selling the mount saving and reloading doesnt matter the mount is still being there near the player after reload lol, even after using an save WITHOUT the 'double mount bug'...
buying and selling any horse will leave that 'cloned ' mount there unsusable untill you sell your actuall mount then you can sell the cloned mount but it spawns again after reloading if you sell that too...
another thing is that apparently the mount cloned IS the horse iv had BEFORE beta 1.60..interesting..even selling reloading, selling alt-tab deleting the save then saving within the game doesnt fix it...odd