Internet Sharing does not work after waking up from sleep

I have enabled Internet Sharing for Airport on my MacBook Pro (OSX 10.5.5).
This works perfectly (for sharing the Ethernet).
Then I put the computer to sleep, then wake it up.
Now Internet Sharing does not work (rejects the correct password from
the connecting device (iPhone)).
I have verified that Airport is on and that the Internet Sharing is still
enabled in the System Preferences.
If I disable Internet Sharing and then enable it then it starts
working again, it's just tedious to do this after every sleep...

(fwiw, it's configured to use 128-bit WEP, Channel:Automatic)