Things are rather fine at present, except that the SPA-3000 does not
detect a disconnect tone from the PSTN line interface.

Of course in PSTN tab I switched "Detect Disconnect Tone:" to YES.

The busy/disconnect tone is 500 ms 440 Hz, then 500 ms silence.
I entered 440@-8;6(.5/.5/1) but there is no detection.
Lowering the -8 dBm detection level does not seem to help :(