We actually already have a solution for this in the works, which will (hopefully) be released in a minor (1.5.x) update in the coming weeks.
As with many other “simple” things, the solution is not so simple when you are dealing with multi-parent. However, we think we have come up with a good solution that should allow permission changes to propagate to (sensible) child cards as you would expect.
It is just always hard to balance convenience with “oops I just accidentally gave someone editor permissions to a card I really don’t want them to be able to edit”.