We experienced some trouble with failed authentications because the user name handling appears to be case sensitive.
It would be much better to e.g. change all user names to upper-case. This is especially tricky when using the LDAP plugin and self-defined users (xml type) in parallel.
Setting repository permissions is sometimes annoying if a user has been added in upper/lower case. The SCM Manager does not warn if you add a user which is not known from it's point of view. If a user is XYZ and you add it to a group as xyz it will accept this without warning, but the user XYZ will not have any benefits of this action.