The fix for got rid of the extra join, but it broke @PrimaryKeyJoinColumn @OneToOne(optional=true) (covered by HHH-4982).
The fix for will simply back out of the fix for HHH-5109.
I have a fix in mind for the original issue (the extra join). I'm not absolutely sure it won't break something else, so I'll create a pull request and get some feedback.
Fixed in master and 3.6.
Bulk closing tickets resolved in released versions