This may or may not apply to this specific issue, but it might spark a few ideas.
In our house, we have an AT&T 962 in the kitchen and a Lucent 965 in the master bedroom.
I estimate about 20 seconds after disconnecting from a call, the Line Status LED on the phones will briefly illuminate and then go out.
I checked the AT&T 962 at my aunt's house and the same thing happens over there. Both houses are being serviced by Lucent 5E C.O. switches, and are in different towns.
I called Verizon on this and they said that it has to do with the 3-way calling feature that they have active on all residential lines. Verizon gives residential customers the option of using that feature on a "Per-Use" basis or by monthly subscription. Verizon said that we could put in a request to have 3-way calling disabled and that would eliminate the LEDs lighting up.