Music Bottom Margin doesn't work properly

Music Bottom Margin doesn't work properly. It should be able to be set to 0, so that bottom line of the bottom system sits on the page margin line, while music "bleeds" into the page margin area.

This is needed so that layout can be controlled perfectly, allowing all bottom systems across pages to be at the exact same position. I would like to add that Music Top Margin works, and we're able to achieve the desired result on the top by setting the option to 0.

Previous discussion: https://musescore.org/en/node/282420