rekordbox / DDJ-400 automatically changing my master when im in middle of tempo mix

Hi Guys,

Rekordbox (or the DDJ?) keeps switching which is my master deck before I finishing mixing in a track.

This is very problematic as I'm pitch shifting down speed on deck 1 to a lower tempo whilst creating a loop build up and then on deck 2 playing a  beat synced loop, so they either go out of sync or i suddenly notice the tempo of both has stopped shifting downwards (as the master has suddenly switch to deck 2 and im pitch shifting on deck 1). its driving me nuts :)

Is there a way I can stop rekordbox from switching the Master automatically til i manually do it at the end of the mix?

Thanks