Whatever happened to hair's shadows?

After a long hiatus I’m back in Blenderland trying out v278c, but hit a huge snag: my particle hair no longer casts shadows. I looked through every setting I consider reasonable and found no new parameters to set (unless it’s in the shader itself, which would be completely illogical), yet in 276b things are fine and in 278c, not so fine at all.


So what (if anything) am I missing?