I tried to fix this in the v1.2.5 update. Unfortunately it is hard for me to properly test this, so we might just have to wait and see. Hopefully the upgrade from v1.2.5 to v1.2.6 will be smooth.
I made sure that whenever Mitch starts, it will remove any dangling “Installing…” installations for itself. So that garbage from your library should be gone now. And I suspect that this garbage is what caused the next update to fail. But again, I’m not sure.