The compositing mode option caused several other bugs. We don't want to support it because of all the other problems it caused. The problem here appears to be a bug in AMD's software, so they'll need to fix that - it's out of our hands, and working around bugs in other company's software by reintroducing a mode that causes a bunch of other bugs is not something that it's tenable for us to do. As ever the best approach is to go to the root cause and get it fixed there.