i tested and even when url path field contains escaped chars. however, i started to get these to syslog every 20 seconds
Apr 10 12:17:08 wheezy1 /usr/sbin/sip-proxy[3900]: ERROR: nathelper [nathelper.c:2018]: can't parse contact uri
most likely due to nat pinging. i haven't checked yet where they come from. contact field of the ua does not have any escaped chars in it.
-- juha