as per Petter Reinholdtsen's suggestion (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=756114#19), adding db_stop in postinst fixed this problem.
as per Petter Reinholdtsen's suggestion (https:/ /bugs.debian. org/cgi- bin/bugreport. cgi?bug= 756114# 19), adding db_stop in postinst fixed this problem.