Yeah, of the three lines in 62a497b, 2 have undesirable changes, and 1 seems to be a no-op (unless there's a particular reason why mount_dy is better than mount_dx).

Having the velocity there  is so that players take more damage from a 60 MPH exit than from a 5 MPH exit. And the TODO comment still applies - they need to *jump* out of harm's way, not be violently flung.