Daf lf 45150 sometimes revvs up when you apply emergency bra?

I have Lf Daf45 150. It sometimes revs up high when emergency braking , that is when brake and clutch are pressed at once. What could be the fault. It also has an ABS warning on dash caused by a brocken wire that should be attached to an abs sensor. Could there be a link between the abs and revving up when emergency braking.