Recently I updated to 1.8, and saw no issues for a day. Today, I see that my audio sources are missing from my control. What is weird is that if I press Group, I see my missing audio sources in there.
Missing audio source:
Pressing Group I can see the audio sources I want!
Aside from, but related to, your issue with zone grouping: I find that some audio options which are shown to be enabled in Settings > Audio are no longer available to be used for playback. No rhyme or reason for which ones disappear as far as I can tell.
Sometimes restarting the server makes them reappear, sometimes not. Very frustrating.