PTC Web Account e-mail address with upper- and lowercase characters

When a user changed his email address using upper- and lowercase characters in his name (part before @), the system was not able to change it, we got this error only:

    ERROR: E-mail address invalid.

Later on i got answer from PTC University supporter, they changed all characters of name to lowercase and then it worked.

I think PTC should correct here something - standard RFC say nothing about such limitations in name of e-mail addresses.