This issue occurs every time for me. My use case consists of using this project: https://github.com/rejectedsoftware/user-auth
Have the user log in with Mozilla Persona and on page reload i noticed the email was looking funky.
parseDietFileCompat!("userauth-persona-auth-mixin.dt",
string, "path_prefix",
string, "authUserEmail")(dst, Variant(path_prefix), Variant(authUserEmail));
Also, i changed authUserEmail's value to something like myemailgmail.com@ and the invalid characters were again following the @ symbol.