Why does the "discard" option have no effect on thin volumes after upgrading to RHEL 7.2?

Issue

• Discard operation for thin volumes seems not to be enabled any more and it is thus impossible to free the space unused by the file system. Mounting the file system with the discard option has no effect, fstrim returns an error:

# fstrim /home -v
fstrim: /home: the discard operation is not supported

• Discard is a fundamental requirements for the correct functioning of LVM thin volumes and it should work.