Well, I'm scratching my head on this one.  I had two instances of reaper running overnight, both connecting to a single primecoind instance.  Both of the reapers now show a nonzero count for the "10-chains per hour" stat.  Based on my understanding of the code, this stat doesn't get filled in until/unless there's a single entry.  Yet there's no record of a "immature" or "generate" (or even "orphan") entry in the primecoind's "listtransactions" output.

I'm left wondering if maybe there's something wrong with how reaper returns work when it finds a block at difficulty?  Or my primecoind is misconfigured somehow?