I tried to get this sorted out in Help but no joy. Since the problem may be a bug…
It’s possible to title a clip with overlay HTML and text filters at the same time. It’s possible to export a frame with the two filters. Rendering the clip, OTOH, doesn’t give both the overlay and text. Only the result from the text filter is in the rendered clip. I tried to duplicate the problem and my rendered file has both titles. Which means, I think, rendering the wrong way causes problems. What’s going on here?