We recently installed this update, and found that half our customers would
lose registration after about a minute. Packet capture shows that the
phone sends the keep-alive packet (a SIP options packet), gets back a
SIP 481 no subscription, then immediately loses registration. Turning off
keep-alive fixes the problem. This is with Cisco/Linksys SPA phones, both
older 9xx series and the newer 303 and 5xx series.