We have a messy AD where not all email addresses are in lower case. Some are capitalized and some are not.
Because of this, a user may login with USer@acme.com or user@acme.com .
I see in the ACLS table that the permissions are stored both ways, depending on how the user was logged in at the time the documents were created.
So, because of this, sometimes a user doesn't have access to basic functionality like edit it's own profile or access the personal workspace.