DDJ-RB Master volume controlling tempo

This a really weird problem but I got a second-hand DDJ-RB controller and for some reason the master level knob is controlling the master volume for both decks but also controlling the tempo for the left hand side deck. The tempo fader for the deck on the left is not working and the only way to control the tempo is using the master level knob. I've never experienced something like this before and i was also having the same problem on traktor after downloading some mappings for it, pointing towards a hardware issue rather than a software one. Anyone experienced anything like this before or knows any solutions before or shall i just return it?