I've just had exactly the same as the OP... 100gbp worth of bitcoin vanished within a minute of depositing. The addresses are the same I notice. There's definitely a security issue here.
13wahvu3FP8LK8P51UmEkhBUhyC7mzkrn3
14ggKdDdr6S4rjkesjWH7Te7AMxJr2Y3xz