Has anyone had this problem? It's happened to me twice, all of a sudden it will not move, but the engine is still running and blades will engage and work. Dealer has picked it up and repaired it twice - says they've never seen this happen before in 50+ years! The drive belt is tearing right through the fan! Bought this mower new about 3 months ago, and this has happened twice - needless to say I'm not happy and am concerned about the durability of the mower moving forward.