Naughty Boy - Bolero / Bluetooth misbehaving

I have an intriguing issue with my Bolero / Bluetooth at present, have searched the forum and can't see any previous comments on this so, before my Yeti goes into my dealer shortly I thought I'd ask if the problem I have is known about and what might be the fix.

I had a Pure Highway 300Di DAB radio unit fitted 10 days ago.  A few days later, checking over the settings on my Bolero I discovered the fader for the speakers set to 'front only'.  I reset this and carried on.

Checking again on next journey I discovered again speakers set to 'front only'.

After some trial and error testing I have worked out that, having switched the Bolero / 300Di on with the ignition all is OK (speakers set to equal front / rear) but when my phone connects into the Bolero on bluetooth, and I get the prerequisite 'bong', the speaker flicks to 'front only'.

A problem though is that I don't fully know how long this has been going on for as I check the settings rarely. 

Is it a bluetooth / Bolero issue or is it related to the installation of the Pure 300Di DAB?  Does anyone have any ideas?

Guy