You can't search for tags that are not in the drop down list of the tag box. If I search for banana, I will not find a collection of the 170 games tagged banana, but only games with banana in their title.
Maybe consider renaming the search result from "tags" to "suggested tags" or other means of clarification to the casual user. Calling it tags might imply that the search bar can exhaustivly search tags. It can't. Also the text in the tag search box is kinda misleading. It reads select a tag, while in truth you can write in any tag, not only the selectable. Took me several months to realize that.
Same for the results of projects, they could read suggested projects or similar, to imply that those results are not exhaustive. It is a shortcut for the x most relevant things, I know that, because I read this post. But will a new user intuitively grap this. I saw threads opened in communty because people did not understand why they cannot find certain things (like tags) in the search box, not realizing that there are two search boxes and that tagging a thing is not enough, they must write the thing in their description.