Time Machine can't find AFP/SMB shares

Question

I have an Ubuntu NAS setup with both SMB and AFP shares, both of which I can access from my Windows machines and Macbook Air. I have also verified that I can copy files to these shares from my MBA.

But Time Machine on Lion doesn't show any of these shares, only "Set Up Other Time Capsule". What do I need to do for it to show these shares?

I've tried defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1 and defaults read com.apple.systempreferences TMShowUnsupportedNetworkVolumes returns 1.