How to stop ubuntu trying to connect to non-existing wifi card after wake-up

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http://ubuntuforums.org – After Ubuntu 13.04 wakes from sleep it tries to connect to the net via WiFi, though there is no WiFi-card in the machine. It stays in this mode until I switch it off. Regular shutdown does not work either, I have to push the power button. The problem is annoying, since my PowerFolder Cloud Software stops synchronizing, even though both gigabit ethernet ports stay connected (but cannot be disconnected from the menu). This only happens after a wake-up from sleep, not when booting. How do I prevent Ubuntu from trying to connect to a non-existing WiFi-card. ifconfig wlan0 down won't do. -- Juer (Hardware)