Not necessarily as an alternative and hopefully easier approach (at least for the time being) is available in the following thread by way of manually applying a potential pending improvement.
@upapi_rockstor in that thread has confirmed this as a work around with the same caveat as you mention, ie the btrfs-usage column.
Hope that helps.
EDIT: As from version 3.9.2-5 the above referenced patch is already applied / included.