I think you are on the right track but missed creating a stationary mask that defines the actual border between the sequences.
I would create a 3rd video track where I'd place an empty Title. Simply remove the Add Text element and add 2 boxes, white and black representing which parts should show/hide. Then add a simple blur effect to the title to create a softer edge.
Finally use the Track Matte Key effect on one of the baggage clips and specify the track where the title is (Video 3 most likely) and set it as Luma Matte. Invert if necessary, scale up the title in case it "leaks" at the edges because of the blur.
Of course you could do a more advanced key element in PShop etc but if you just need a clean vertical, feathered edge where the xray bag appears, this should be enough.
That's pretty much one of the techniques I tried. I redid the whole thing in a new project and used this procedure but unfortunately without success. The mask in track 3 still follows the motion path of track 2. Even though it has no path and is centred on the screen, when it's played back the mask starts off screen (as does track 2) and just tracks across the scene, masking the same part of the bag throughout.
Thanks for your assistance.
Ah, you have a motion path on track 2? Seems the software automatically lets the luma mask inherit that motion as well.
I thought you had 2 static, non animated video sequences... this is pretty tricky (in PE). Have you tried "canceling" the motion by copy pasting the motion/rotation keyframes from track 2 to track 3 then reverting the actual values? It could fail if PE cancels that too but it's worth a shot.
Thanks for opening up that avenue. There's at least one work around that should work. As long as the matte has it's own motion path, and maybe in this instance some scaling too, rjough I haven't tried that yet. I tried a one pixel motion path and it was just ignored, but longer paths worked. Might need to objects, willl nut it out next weekend. Thanks for your advice.