The list of demos is evidently supposed to be sorted in chronological order, but on a Linux machine, I've never noticed anything like that. Instead, it seems demos are sorted in no particular order I can tell, but always the same order every time so it somehow is a deterministic procedure.
What's more, after playing a demo through to the end, the game returns to intermission and pops up the voting menu, but now with a phantom entry in the "recently played maps" section of the list. I don't think the particular demo matters, but I tested by playing back the "cyanide41458.dmo" file from on three separate occasions from a freshly started program each time. For me, this demo shows up in 79th position on the list, out of a total 86, and it caused a different map to show up as recently played each time: longestyard2k, livefire, and canyon (never cyanide, strangely enough).