Phil,
It's possible this may be a "Cotton Issue" variant, but, I've seen the 1st Texas' cotton flag in Austin and the proportions are different. The bars on the Texas flag are wider and the stars are larger. The Mississippi flag in question looks more like what you'd get if you crossed a cotton issue ANV with a third bunting issue ANV. Examining the flag, it appears to be made of bunting. The description says that it was brought home from Appomatox. I'm assuming they meant at the end of the war. What peaked my interest is that I had read that by that time the ANV had pretty well weeded out all of the non-standard flags and replaced them with Richmond issue flags (either battle flags or second nationals). I guess this would be my application to the Department of Confederate Flag Speculation. :-)
Charles