@eschwartz: Yep, the staging directory not being cleared on error is a bug, will fix
.
And, yep, the mntroot issue is also a bug (you have AcxE installed, I haven't, my check was too dumb to take that into account).
In the meantime, do restart without running MRPI, because your rootfs is currently rw!
Il'l fix that when I get back later this evening, thanks
.