I have this problem as well. It appears that the default route gets deleted before the connection attempt is made; I click 'connect' in Kvpnc and instantly it says 'No network reachable'. 'route -n' then shows that there is no default route, hence the OPs 'fix' of ifdown/ifup. It seems to happen about one time in ten, I shall endeavour to get some debugging output and post it.
-- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org