Changing the password with 'smbpasswd' as a local user on a domain member doesn't work. It fails because it tries to lookup the user using winbind. It doesn't try auth_sam. Patch will follow.
Created attachment 13494 [details] patch for 4.7
Created attachment 13496 [details] patch for 4.6
Reassigning to Karolin for inclusion in 4.7.0, 4.6.next.
Pushed to autobuild-v4-{6,7}-test.
Pushed to both branches. Closing out bug report. Thanks!