Another comment from the "victim"...
My M9 didn't start deleting files...I'll have to go back and re-read what I wrote. What it actually did was begin CORRUPTING the files, so that they were unreadable, either in-camera or on the computer in any RAW-reading software.
But the gist is the same...the camera locked up, and spontaneously started corrupting files (rendering them unusable...essentially the same as deleting, as far as I'm concerned...they were unrecoverable by me).
After I finally yanked the battery out (because it continued it's diabolical work, along with a blinking red light, when I switched the power off), I regained control, since it was dead. I reinserted the battery, powered on, and the camera told me the battery was low. I switched to a charged battery, and a new card, and it operated normally. Remember, I was ankle-deep in sand on Ipanema Beach, not the best place to perform troubleshooting.
My research online since then indicates that many issues, possibly related, conspire to make this problem occur. The card has been used, and was previously being used in camera, so the card is a good card. I had taken about three shots in succession, and I usually wait for the blinking red buffer light to stop, but since it was buffering multiple shots, I assumed I could see the first shot. That's when it lost it's little electronic brain and malfunctioned.
My issues with this are basically, 1) a camera should NEVER corrupt previously-recorded image data...ever, and 2) if it's related to battery-low states, what good is the battery low indication if it craps out BEFORE you get the indication? Again, I have spare batteries, but how do you guess when to change a partially-discharged battery?
As far as blaming the victim...yes, I assume some responsibility. I am mostly unfamiliar with the M9, and my previous experience was with an M6 (although I've got plenty of familiarity with digital cameras of all kinds). The firmware in my M9 was 1.62, not the most recent. The firmware is now updated. I'll stick with it, and shoot my M9 on my upcoming trips to San Juan, Puerto Rico, and Paris. If it recurs, I'll be switching to my 5DmkII and selling the M9. I don't mind changing my method or speed of shooting for a different kind of camera, but it's hard to justify the expense for a crippled piece of man-jewelry, if that's what it becomes.