Cannot insert photo (JPEG)

For some reason, this 640x480 project won’t allow me to insert a 640x480 JPEG (or PNG) image into the video track or even on a new track. What’s going on? What have I missed? I’ve done this many times with other projects…

Never mind. I tried adding an audio clip to a new audio track and came up with the same problem.
So I saved the .mlt, closed Shotcut then re-opened the .mlt. Everything working again.
Memory leak?

This is related to this bug: