TheMarshmallowBear
Benelovent Chieftain of the Ursu Kingdom
Agreed, it's happened too frequently for it to be chalked up as map editor shenanigans. Perhaps there's a civ4-like mechanic where mines had a chance to discover a mining resource: once a farming resource is worked for a while (ie, the civ is knowledgeable about it) it can be "discovered" that a tile is particularly fertile for the crop.
Fwiw, that's how I have always justified unmovable/unpropigatable resources in civ games - it's not that wheat (or whatever) isn't grown on regular farm tiles, it's that the tiles where the "wheat" resource exists are just exceptionally productive spots for it.

I would hold any "evidence" until we see ACTUAL long-term gameplay footage.
The E3 demo really should be taken with a grain of salt to its intricate details.