I have a user that I want to grant access to a site in a given site collection.
When I search for that person in the people picker I can find her in the address book and then click to add her to the permissions dialog but when the permissions dialog populates it shows somebody with a different Account Name.
The Account Names are similar and are just different by the number at the end of their account name. In Active Directory these accounts are two distinct people.
I have noticed that if I try to grant the same person access to a site in a different site collection then everything works out fine and the name does not get switched when granting access.
I have confirmed that this Site Collection is not set for read only. Also I found the user in one of our content databases and the IsActive flag was set to true for her account.
Our User Profile sync is set to run incrementally every night and then fully once a week. This persons account has been around long enough that it should have already been through both of those sync jobs.
What could be the cause of this problem?