Why on the earth do you require people to remember their username while they have forgotten their password?
Isn't the email address enough to verify ownership?
And if the user has forgotten both the username and the password, how do you expect them to recovery their account?

Yes, unfortunately I am one of those stupid users.

We're aware that the current KDE Identity software has some shortcomings. At this time, a rewrite which will bring numerous user experience improvements is underway, but it may be a while before it is deployed.

If you have any issues with your Identity account, please send an email to sysadmin@kde.org and they'll sort out your problems.