I found when i set my clone's /maxfpsbk to 10 or lower, they would come off follow quite often. I currently run with maxfps 30 on main and maxfpsbk at 15. When I know Orgrimmar is gonna be bustling with people, before I run into the entrance i will take all my clones, zoom into first person view and have them looking directly down at the floor.

That way there's really not much that needs to be drawn on my clones, and I run up to the mailbox/auction house without issue, and everyone following along.

Shattrath is another story all together...I wish we could turn off some of those hundreds of damn NPCs.