Try going in incognito and hit register. Email being hidden is ticked.
This issue was fixed, long, long ago.
Try reading the posts above in this thread. I already said that the checkbox was checked, but after registration the setting immediately goes to automatically showing. I created a test account; try creating one as well and you'll see what I'm talking about.
This is almost 100% a bug. I went through and created an account from scratch (
here); the checkbox for "hide my email from the public" was checked by default, but when I created the account the setting switched to being public automatically.
This is a bug that needs to be fixed.