GetUser: differing overload calls returns different username case

HI,
During my development I've noticed that depending how I call the Memberships.GetUser method determines how the username is returned. I only have two users in my Database right now:
"John"
"Michael"

If for example I call Membership.GetUser("John", false);
It returns with the MembershipObject and the Username correctly as "John"
If instead I supply John's providerUserKey then it returns the MembershipObject with the username "john" (all lowercase) instead.
 
Is this a known issue? If not could someone please verify the problem and perhaps suggest a workaround?
I use the UniqueId to link records to the Membership so it doesn't look right when I output the username at this time.
 
Thanks,
Luca

 
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