PiP operates correctly in timeline, but is ignored in export

I need to overlay footage of a timer over another video file. For that reason, I want to use shotcut composite the timer onto the video file. Using the Size/Position filter, I succesfully set what I want the frame to look like, and the software displays it successfully in the timeline view. However, the exported video does not show the topmost video track (the timer), only the larger video file. Is anyone else experiencing this issue? It is a very big annoyance to wait a half hour to find that the exported video is useless.