Mailing the story:

Incompatibilities among "copyleft" licenses meant to promote the sharing of creative work could end up preventing it, says cyber-law expert Lawrence Lessig. The problem is that the copyleft licenses, like the "free software" licenses from which they're drawn, require that derivative works be licensed under identical terms. And those terms differ from license to license.

[ED: Lessig is someone I take seriously, hence, this is a disturbing problem. Nonetheless, not one that cannot be resolved (perhaps with fewer, simplier licensing conditions?). These are important issues when trying to match dissimilar content, e.g. text and audio/visual becomes contentious. - HC]