problems with choosing a forbidden password

The password I chose for this account was not allowed by the rules that pop up in a box when a forbidden password is typed. Nevertheless, I could save my choice. However, when I tried to log in, neither the new password nor the old one was accepted.
When all the characters I type are spaces, I am told to enter a password instead of that the password is wrong. This happens if my chosen albeit forbidden password consists only of space characters, too.
When the password I typed to log in was not accepted, I was asked if I forgot my password. I clicked on that, logged in via the link sent to my e-mail, and chose a password that was allowed by the rules. I do not have any problem with logging in anymore.