If you enter tags that don't exist (and you don't create the tags), press Post Your Question, view the tag related error message and then remove the offending tags, the site continues to think the offending tags are there when they are not.
Clicking on Post Your Question simply causes the page, with the error message shown, to be re-displayed. The only way to post the question is to discard it, start over and avoid entering the offending tags.
