Looks like the scratch build fixes the issue. I was able to reproduce this by simply running /usr/libexec/nfsrahead /dev/sda.
(2.8.6-0.rc1 also fixes another nfsrahead issue introduced in 2.8.5 where the command takes 10 s to finish so I hope we can get the fix released as soon as possible)
This update has been unpushed.