Being able to load standard MP2 titlepack maps in regular MP4 titlepacks. <--This is good.
Being able to load env-mix MP2 titlepack maps in regular MP4 titlepacks. <--This is bad.
I was playing regular MP4 Valley tonight, and loaded an unplayed map from my downloads folder and found various CPs that I could not complete. I eventually realized that it was an MP2 titlepack valley map that used the Lagoon car.
Ideally, one of three things should happen:
1) MP2 env-mix maps should not show up in the maplist when browsing from an MP4 station, or
2) There should be a warning displayed that indicates the map is env-mix and may not work properly unless loaded in MP2, or
3) The env-mix option should be supported in MP4, assuming the player has the required environments (and they should see an "unable to load" message explaining what the problem is if they don't).
#1 would be pretty quick and low-effort while we wait on #3...

Edit: Added some clarity re: game version vs. titlepack