[LAU] nanokontrol and go to start of session

I'm using Ardour 2.7.1 on Ubuntu and just hooked up my Korg nanokontrol control surface I assigned the faders and buttons to the mixer faders and solo/mute buttons with the ctrl+middle click no problem works like a charm I then assigned the play and stop buttons again no problem it starts and stops the playback as expected the problem: when I assign the 'go to start of session' on the transport section to the return button on the nanokontrol it didn't work ditto on the 'go to end of session' assign and usage an 'operate controller now' box did come up and when I pressed the 'rewind' button on the nano it disappeared but neither the 'return' or 'end of session' buttons function when pushed anyone know what I'm doing wrong here?