I have been using Safari on OS X for a while without much issue until I hit the one described in the title.
Let's say I have a YouTube tab open. If I hit the new tab button and enter YouTube, instead of opening another tab, Safari redirects me to the existing YouTube tab. It is not limited to this website, Stack Overflow behaves the same for example.
I could not find anything in the settings related to this and Google didn't help either.