[&UserID] for some users it returns their account as all lower case?

My AD account has mixed case, several other users do as well.However, for at least 1 user I am aware of it returns their account as DOMAIN\username instead of DOMAIN\UserNameI can't figure out why that is. In AD their account is User Name.I don't suppose anyone has run across this issue?I can use a to Lower or To Upper to work around, but would like to understand the root cause.