The system for these isn't working. Instead, it leaves the character stuck and unable to cast anything. The only solution to it is to relog.
Horde Siege Tanks, in Borean Tundra, used for The Plains of Nasam (http://www.wowhead.com/quest=11652)
The Rebel Cannons in By Blood and Ash (http://www.wowhead.com/quest=14218)