Safari search bar doesn't lose focus on Enter
Unfortunately this is one of the small unnoticed things that I accepted to live with. This issue has been going on for years. 

I tried to bypass the issue by installing an extension from the safari extension gallery that performs searches and those work for some time and the issues ultimately comes back again.

Edit:

As of Safari 13.0.1 in macOS Catalina, I don't experience that bug anymore, seems good so far