Comment 4 for bug 322434

That was what I wanted to know. I just tried to make sure that the correct crypto module was used. Looking at the loaded modules it is clear what is going wrong. Just not exactly why. There is a separate ieee80211 stack in linux backports modules which normally should only be used for drivers there. But in your case it gets loaded and bound to the ipw2200 driver. As a work-around you can add the following line into /etc/modprobe.d/blacklist:
blacklist lbm_cw_ieee80211
then rebuild your initrd with "sudo update-initramfs -u". After rebooting the wireless should work again. Or, if you do not need any driver from linux-backports-modules you could remove that package.