Since the recent macOS 10.14.4 update which includes Safari 12.1 (14607.1.40.1.4), last started to automatically submit web forms with login & password fields once a value for password or login is selected from auto-fill options. This seems to be related to the new 10.14.4 feature where Touch ID got an option to confirm auto-fill in Safari. However I have it switched off but Safari still does this crap. I'm curious if anyone else have the same problem and how to solve it.
UPD Starting Safari 13.0 (14608.1.49) auto-submitting is disabled!