Not sure where to report this, but it feels like a bug.
When putting in my login information, I can use any kind of capitalization I like. I could login as maxastro, MaxAstro, or MaXaStRo and it will work fine.
However, character ownership in a campaign pays attention to capitalization. So if I previously logged in as MaxAstro, and then I rejoin the campaign as maxastro, I no longer own my characters.