My network is properly set up for IPv6 internal and global connection (aka having an IPv6 router).
Since I've upgraded to 12.2 NetworkManager reconnected every 20 minutes (the 20 minutes are most likely determined from timeout values of the IPv6 router advertisement and might differ for other users).
This is actually critical since that means I'm losing my VPN connection every 20 minutes. I only use "Major" because the interval might be longer for other people but basically everyone using IPv6 with autoconfiguration will be affected I guess.

My log shows quite some messages like this:
ICMPv6 RA: ndisc_router_discovery() failed to add default route.

So I found on the net:
https://bugzilla.redhat.com/show_bug.cgi?id=785772
http://cgit.freedesktop.org/NetworkManager/NetworkManager/commit/?id=77de91e5a8b1c1993ae65c54b37e0411e78e6fe6

To verify I've updated to NetworkManager 0.9.6 from G:S:36 which shows no unexpected network reconnects for the time being.

I strongly recommend to either backport the fix or update to 0.9.6 on 12.2.