I can't mount in cities

I can't mount in cities. Im mount and it immediately dismount. I tried in Ironforge and Stormwind. This bug already lasts the second day. That started when i teleported to Mystic Ward in Ironforge with my mage teleportation skill. Im out from the hall and that bug start. Cleaned the cache folder , turn off addons - does not help. In some parts of the city I can mount, for example in the center near the auction. But not in the entire area, in some small areas.
Please help fix it. Icecrown server.

When I use Presverly Holly from the gift box - I can mount as usual anywhere. I cancel this buff - again I can not.