Cannot login using email, only using username

Hello!
I did notice only today that I am unable to login into various sites, installed by various people (so not just my sites), using the email.

I can login into all of them using the username. We tried several users, and username and passoword do not fail.

But it is not possible to login using email and password.

We tried to create some new users, manually or via import (Import via CSV plugin), and again, the username works, the email cannot login.

Does that happen to others?