No, this dongle has a SiliconWave chipset. This chipset implements the 1.2 spec, but Bluez implements 1.1 only. Specifically, on the 1.2 spec the Add SCO Connection is deprecated and indicated as 'not to be used'. The Bluez code (net/bluetooth/hci_conn.c) uses that command to start a SCO voice connection to a headset. I'm suspecting that the dongle doesn't implement the Add SCO command properly and causes my problems. But nevertheless a 1.2 spec device is not required (and is even discoraged) to implement it.

The hcidump indicates that the connection is established but on shut down (when the SCO socket is closed) a first disconnect exchange is concluded but SCO data keeps coming in. The Bluez code complains about those packets (in hci_scodata_packet) and only after a second disconnect exchange does the SCO data stop.

I'm now trying to use the Create Synchronous Connection (as per 1.2 spec) instead to see if this works.