I've got several UBNT devices all running EdgeMax 1.7.0
It appears that they escape the sysContact (and a few other fields) in quotes even if they don't have spaces in them. Observium seems to eat the first one properly but not the second.
snmpwalk -Os -c public -v 2c router01 1.3.6.1.2.1.1.4
iso.3.6.1.2.1.1.4.0 = STRING: "\"
hostmaster@arbor.net\""