I have a few different players around the house, plus a Beam with 2 IKEA Symfonisk rear surrounds.
While I was part of the beta testing group I noticed that at times the surrounds were out of sync with the Beam, but only for music.
For other reasons I went back to the stock setup and left the beta.
A few days ago I was listening to some music in the kitchen but then went to do some housework so set Sonos to play everywhere.
When I got to the living room, the rear speakers were out of sync with the Beam so there was essentially an echo.
As I had done during the beta, I suited diagnostics then emailed Sonos support about the issue.
The bottom line from Sonos is that this happened because the Beam wasn't the group leader, or originator. Playing the source via the Beam and then grouping the rest of the house will apparently stop this from happening.
Now, is it just me or is that pretty poor? The whole point of Sonos is in part its ability to play synchronised music to whatever zones you want, without having to think where you should start the music and then group from. With this admission from Sonos they have essentially broken that USP.
Sorry for the rant, but it's very disappointing that Sonos feel that is an appropriate solution.