How to fix "no WLAN after resume" problem in Ubuntu/Hardy

I have experienced problems using WLAN after resume from suspend in Ubuntu/Hardy. More precisely the wlan0 link came up and was usable for a couple of minutes. Then the wlan0 link was still available but no data came through and not even a simple ping ICMP request was possible. I assume the same problem occurs not only with wireless networks but also with wired networks (ethernet/eth0). My investigations revealed that the problem came up because I use a custom network configuration which is described in /etc/network/interfaces . Apparently such configurations conflict with pre-installed (KDE's/GNOME's GUI based) graphical network configuration tools which I do not use. Removing these tools solved the problem for me:
aptitude purge network-manager network-manager network-manager-gnome network-manager-kde network-manager-openvpn network-manager-pptp network-manager-vpnc networkstatus
Probably you do not have to remove all of these packages but only a few of them.