Never saw this on my test domain, but when I joined a new install 4.2 devel edition server to our domain today for some testing before moving passing mail over for usage, it reset all users UID's and GID's. This totally screwed up file access on all network shares and roaming profiles.
Looks like my holiday is down the tubes.
PS : Fresh install of 4.2 downloaded Monday. XenServer 6.5 vm. Domain has multiple samba 4.2 servers in production. Change occured during the first setup when joining as an additional domain controller. My monitoring platform shot out warning for uid and gid changes to every user and group on the domain as the saving module settings message was up.