Filesystem corruption when installing ReactOS on an existing partition

I just tried to install "reactos-bootcd-0.4.8-dev-483-gf941c78-x86-gcc-lin-dbg.iso" over my existing ReactOS installation as I have always been doing. But the installed ReactOS doesn't boot up, failing randomly with "Error loading NTOS core", "Can't load boot driver", or even not getting into FreeLdr at all.

I bet this is related to what I read on #reactos-dev two days ago:

[22:10:05] <hbelusca> hmhmhhhhh updating ROS installations now fails silently, and passing the hard-disk under windows' checkdisk shows that each file has a "truncated first entry"

Regress-testing currently yields:

reactos-bootcd-0.4.8-dev-440-gbd1e7bf-x86-gcc-lin-dbg.iso WORKS
reactos-bootcd-0.4.8-dev-483-gf941c78-x86-gcc-lin-dbg.iso FAILS