Yes, this was an historical problem of previous versions of BH if installed in flash, but I supposed it had been solved: it automatically detects the /media/hdd to watch already recorded files but it was unable to use for new recordings because it cannot succeed to mount it.
It seemed to succeed but, after the restart, everything was as before...
I can't check it now (I, too, have BH 3.1.0 in OMB): is it still the same? It seems so, from your post.