You could test it yourself with a cheap volt-ohm-meter.
It must be a old instrument, with a needle instead of a digital readout.
You may get one on hardware stores and electronic shops.
Use the DC scale, and put the voltimeter across the two phone wires in paralell when there is a call in progress.
The reading should be around 15 to 30 volts, dc. When the remote PSTN person hangs up the line, the needle should peg all the way on the other direction for about a second or two, before returning to a normal voltage of 48 or 60 volts, depending on the equipment used on the central office .
If you do not see that, you will need to enable tones supervision, trying to get the disconnect by making the Quintum “listen in ” into the conversation and disconecting the line by listening for the interrrup tone that happens a the end of the call.
Post back your findings!!
PS At least on the old Tenor, you could not have tones supervision on anything but “loop start”
If you have reverse battery or polarity reversal “on”, the tone supervision will not work.
You could select them, but they will not operate.