If dfs root share (msdfs root = yes) has path set to e.g /tmp everything works just fine. Once you set it to /tmp/%u, to serve dfs root different for each user you get directory not accessible message on windows client.
Bug reported by Jacek Stepniewski <jacek.stepniewski@agora.pl>
%u substitution cannot be used since Windows client connects to dfs root share anonymously. Actual logon is done when connecting to dfs node ie. a server's share. This first GET_DFS_REFERRAL provides no information about user credentials.