Password changes itself after login

I’ve just installed WP 4.1 on a Windows server with Plesk. It was installed via the Plesk control panel. No problems there. I was able to login once as admin after the initial install but not after that. I used phpMyAdmin to reset the admin password as discribed in the support forum using MD5, enter a new password, then save. When I refresh the db view, the password indeed was encrypted. In another tab I try to login using the new password; as originally entered, but it fails with no error message. I again go back to the database and refresh and the value has changed. It looks like the MD5 encoded value was encrypted again.

Any ideas?