I happened to notice my regular WordPress tag archive pages come up empty for tags that have no events associated with them, even when regular posts are tagged with that particular tag.
For example, this tag, which is actually used on 19 posts but 0 events, comes up empty, while this tag is used on 21 posts but only returns the two that happen to be events. (You'll also notice the tag archive page has "Events List" in the <title>.)
Best guess is it's a conflict between something I've done and TEC, though I'm having trouble testing it because turning TEC off breaks my site. (Obviously my own issue there.)