Just to nip this in the bud, no--I wasn't using one battery to power more than one device. The R-44 was running on four AA cells in its underbelly (I changed them during intermission), while the V3 was running on a separate rechargeable battery of its own.
The interference problem, if that's what it was, first appeared as a buzz in one channel of my stereo mike, which was plugged directly into channels 3 and 4 of the R-44, running from the R-44's internal phantom powering. I swapped the two XLR plugs and the buzz changed to the other channel, so I thought at first that either the mike (an older model which was recently overhauled) or the cable was defective. I found an odd way of looping and running the cable from that mike so that the noise was minimized, but it was still audible over headphones.
I promised some weirdness and here it is: I moved some of the stuff around (R-44, preamp, preamp battery and the respective cables between them), during which time I powered down the recorder. When I powered it back up again, suddenly the buzz was in channels 1 and 2, which were being fed into the recorder digitally from the outboard preamp/converter. Channels 3 and 4 were perfectly quiet; it was as if the poltergeist had simply moved over.
Eventually I moved the preamp/converter's battery, the preamp/converter and the R-44 as far apart from one another as their cables would allow, and at that point I no longer heard any buzz, and I left things that way for the whole concert.
--best regards