This appears to be a subject that Clem and the development team will probably address soon enough. LMDE is a different animal from the Main edition, so the old way of doing things will most likely need some slight adjustment.
The noted Level 4 and 5 updates have caused no issues in my pure Debian install, but I have not run them in my LMDE install yet. I honestly do not foresee any glitches, but with a few people in the forums already posting problems, all bets are off.
Linux Mint Xfce 64-bit and Debian 6 "Squeeze" GNOME 64-bit