7D shutter too slow above 1/2000'

Anybody else have this problem?

Up to 1/2000' everything is fine.
At 1/2500 I get a partial image.
Above 1/2500' I get all completely black.

In manual or Tv or Av, with iso 100 to H, apertures 1.2 to 22.

EG whatever the settings that give me a perfectly exposed shot at 1/2000', if I bump ss up to 1/2500' I get a partial shot. At 1/4000' (having opened up a bit to compensate), all is pitch black, now amount of P&P can get a peep out of it.

Anyone else have this ?