@Alaska After reading your explanation I agree with you. It looks more like a design issue than a bug. Thank you for that solution, it's really helpful when using the add-on "Animated Render Border"
I found a temporary solution by creating a box mask almost the same size of the render region and aplying it as alpha for the shadow catcher pass. Also the "Alpha" option MUST be enabled on the…
This is what it happens when mixing for example with a color.
Can confirm it's black, not sure if it's a bug, to me this is just colors that are not written.
I don't see it matters anyway since only visible part of the image is relevant anyway?…
Temporary solution....
-add a custom property to any object, -add keyframes to that property -right-click copy property as a new driver -right-click paste driver over "Opacity", "Restrict…