ID change only works if I make one letter upper case

I am trying to change my ID back to Konflixx, which it was in the past, now whenever I try to use that name it tells me it's not a valid ID. However, if I change the spelling to KonflixX it will work no issue. I then try to correct the spelling, and it tells me the name is already in use.

I am at a loss here and I hate the way it looks with the xX.