Login with password manager not straightforward

[SafeOnline]

I use a password manager to login to all my accounts.  When I click on the efmer.com link my username and password are pasted into the required fields, but the words Incorrect Password appear in red at the top of the login box.  I have to copy the same password from the password manager, and paste it into the password field before clicking on the Login button works.  Is this a security feature or something else?

[fred]

Is this a security feature or something else?

If you mean this forum, it's the password manager.
http://www.simplemachines.org/ is one of the most used forum software. I don't have any problems with my manager.

[SafeOnline]

There is one other site, www.att.com, that just recently started deleting both username and password a moment after both fields are filled in.  Since that is new behavior it most likely is site specific.  My password manager resides on the server of an online security company.  I can message them to get their take on the issue.