802.11 decryption

Like a few other posters, I'm not able to decrypt data captured from my wifi network.

I have:

• Entered the key into the IEEE 802.11 preferences, in the wpa-pwd:KEY:SSID format.
• Turned on Enable Decryption in the IEEE 802.11 preferences.
• Tried all combinations of FCS/protection bit.
• Ensured that I have captured the handshake by:
• Disconnecting and reconnecting a client.
• Confirmed EAPOL packets in the capture: I see 1/4, 2/4, 3/4 and 4/4 on the expected addresses.
• Sanity checked by decrypting the capture from http://wiki.wireshark.org/HowToDecrypt802.11 - worked fine.

I really do think I've ticked all the boxes on this one, so any help would be appreciated.

Wireshark 1.6.7 on Ubuntu 12.04.