Running videos side by side does not work in latest shotcut version

Hi, I’ve been using the latest version of shotcut on linux mint 17.2 and have tried to run one video inside another using two video tracks and the size and position filter. However this does not work, only the top track’s video is visible and the bottom track is blacked out. Any thoughts? Here’s a screenshot:

You have failed to enable ‘composite mode’ on the Track V1.