I think Shotcut is working as expected in this case. Remove Crop Source from V1. Add a secondary track, V2, On V2, Open Other - Colour, select Black and apply 2 Mask Simple Shapes, one for top, one for bottom. It does work but I’m sure others may be able to supply a slick solution.
Unfortunately it does not work exactly like “Crop: Source” and it is way more complicated to achieve the result I want. Crop needs only one simple mouse shift.
When sliding the bottom-controller up in Crop, it adds black bars on bottom and top. But it cuts off only the bottom part of the image while the upper end of the image remains. The image itself shifts down, so to say.
When working with masks the transition from a black bar to the actual image is a bit blurry, not sharply devided as when edited with Crop. But this is not that important.
As non-native speaker it’s hard for me to describe precisely, hope this all makes sense.