Register Plus custom logo distorted

Since upgrading WP and Register Plus to the latest versions, the custom logo at login page is there but “compressed” vertically. I tried to change the image but all my blogs have exactly the same problem. Did not find a way to make the image “normal”. The image is all compressed near the top and under it is white space. Others have upload problems, in my case no.
See one: https://www.beijing1980.com/wp-login.php?loggedout=true