Strange. I personally can't recall anybody reporting Norton to raise false flags on any MB 3.4 version before.
It would probably be good to report this to Symantec/Norton. It's obviously a problem on their side.
Anyway, I just ran the latest MusicBee 3.4 beta .exe through VirusTotal.
Hopefully that proves to anyone stumbling upon threads like this one that MusicBee's trackrecord is still perfect after all these years.
(as long as you download it from MusicBee's website of course)