I can't comment on DFX2 (I don't have the game), but I know that in DFBHD, there is an absolute limit to the number of items you can have entries for in a .mis file, and for some reason, tiles actually counted toward that limit.
According to my notes:
Code:
16:06 30.09.2008
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MED Item limits
In one map, you can have:
Buildings and Decorations 1200
Vehicles and Objects 1200
Markers 768
People 256 (including players)
Tiles 6144 (minus sum of the above)
But no more than:
Vehicles 64
Events 255 (I think)
Is it possible that DFX2 has similar limits?