You have to click search again, not sure if they have any plans on changing it but going to the search page (Either as a link from a certain tag or by the search button) it'll not actually use your excluded tags (Look at the URL before and after pressing the search button, it changes), my recommendation is make a bookmark with an empty search (As in go to the search page, and just hit search to have your excluded tags actually excluded) but I don't really know if it's worth the effort in all honesty, do see how you can be confused since the UI shows that the excluded tags are "excluded" but it's no actually used by default.
But yeah, TL;DR just hit search once and it'll fix the issue.