Offline processing preview doesn't work as it should

I all,

I’m currently working on a 5.1 editing session, and while doing some offline processing, I noticed a very strange behavior of the preview button. The sound comes out on EVERY channels of my monitor setup, even if the original clip is mono or stereo… As I make a lot of offline processing, this is a very annoying problem, I just can’t use the preview…

Any workaround to fix it ?

I found a workaround : I have to solo the right set of speakers (i.e. LR, or C) before making the offline processing…