I work with a software that grabs the account username of whoever is logged in and adds it to an access database when our software is opened. For a few of the customers that are using our software, the case of their username sometimes changes when they log in (for example, "UserName" vs. "username"). When these customers log in (from what they've told me, anyway), they are selecting their account, which automatically selects their username and they don't get the option to type it in.
So my question is... What would cause the username to change case when logging into Windows?