Plesk 12.5 protect with htaccess?

In Plesk I have set a htaccess protection for the admin panel. Source: https://talk.plesk.com/threads/protect-plesk-panel-11-5-with-htaccess-auth-basic.291451/#post-702210

Now after upgrade to 12.5 this not working properly. The AuthBox appear, but after click and not before and I can working in Plesk with cancel the AuthBox. Is here a workaround to fix this?

I want protect my plesk panel with a basic auth box.