Is Absolute Position supposed to disable 'Scale' and 'Left and Right' constraints?

I have an auto-layout frame with a fixed width (the screen). I like to resize it every now and then to check how everything looks in different screen sizes.
Inside it I have another frame (a translucent navbar/header) set to absolute so it sits on top of other elements. However I want it to always match the width of the screen. As soon as that’s changed, I have to manually fix the header each time.

I’ve found some related threads (1, 2) that seem to have a similar issue, but it seems they’re bugs and the workaround is to set the position to “scroll with parent”. In my situation, the element is already set to it, so they might’ve have a different problem.

What am I doing wrong?