[SR-Users] about destination blacklisting

i made a test where domain name in request uri hostpart has two udp srv records, one with higher priority than the other. when i turn off the higher priority uac, there is about 5 sec delay before the lower priority uac starts to ring. if i make another call within a small number of seconds from the previous one, my sip proxy remembers that the higher priority uac is dead and the lower priority one starts to ring immediately. but if i wait about five seconds or more, my sip proxy again first tries the higher priority uac and there is again the about 5 second delay before the lower priority one starts to ring. i have in config use_dst_blacklist=on dst_blacklist_expire=20 from the docs i get the impression that my sip proxy should remember 20 seconds that the higher priority uac is dead, but it only remembers it about 5 seconds. what could be the explanation? -- juha