Just like after UP4, UP5 installed Nautilus as one of the 1300+ updates, even though I did not have it installed initially, and did not ask to have it installed.
When it happened after UP4, I put it up to me having somehow installed it by accident, but after the hassle it caused me before I had completely removed it, and here it is coming back in again. I was able to fix it quickly, but I think the fact that whatever bug in mint-update-debian caused this to happen still has not been fixed has everything to do with the glacial rate of LMDE updates. I have added nautilus to the Update Manager Ignore list but really: how hard can it be to include a bit of smarts in the program that prevents it from installing an update package that is not present?
I still really like LMDE, and the concept of a rolling release, but at this point it is painfully obvious that the project just doesn't consider LMDE a priority, and while I am not ready to chuck it and look for another distro, if this happens with UP6 (whenever that is; at the rate of release it'll be April of next year at minimum) I will be quite unhappy.
(the symptom for me is that gigolo opens a share using Nautilus, rather than Thunar, and that in turn causes the look of my desktop and the gdm2 login screen to change radically, and I have to do a killall nautilus to get things back to normal)
I just wanted to share this with the group, and I do greatly appreciate the Mint Project Team's efforts even if I point out their weaknesses.