So apparently two other people on THR have had similar problems:
I had some trouble with my Rock Island because of the hammer following the slide and some double-taps on this account.
On disassembly, I found some burrs on the disconnector right at the parting line which occurs with investment-cast or MMC(?) production. These burrs interfered with proper action of the disconnector.
I polished off these burrs and slipstoned some other sliding surfaces and had no trouble henceforth.
I had the same thing happen to me with my RIA last year. I was at home and I usually change out my mags on a weekly basis and I had just put a fresh mag in the gun and released the slide lock and the gun discharged just missing the cats and putting a big hole in the wifes cedar chest. I got rid of it ASAP.