We can confirm this Bug (Debian 8.0 Jessie on VM host and guests).
os-prober version: 1.65 amd64
VM host
=====
Sep 7 14:43:19 vm-host os-prober: debug: running
/usr/lib/os-probes/50mounted-tests on /dev/mapper/vm1-disk
Inside VM1
=====
Sep 7 14:43:20 vm1 kernel: [4552906.712287] end_request: I/O error, dev
vda, sector 5125812120
We had two out of five EXT4 VM filesystems corrupted in a single run of
"apt-get upgrade". The filesystems automatically switched to read-only
mode shortly after the first errors and we rebooted both VMs (fsck
automatically enabled: orphaned inodes and some inodes had to be removed).
We regard this bug as highly critical.
