• Add 0.18.3 as a dependency of another mod which uses Natural Evolution Enemies.
• Load parent mod and restart game
• Error message is shown, blocking factorio from loading:

Failed to load mods: The given sprite rectangle (left_top=0x0, right_bottom=64x64) is outside the actual sprite size (left_top=0x0, right_bottom=32x32).
If this is being used as an icon you may need to define the icon_size property.: Natural_Evolution_Enemies/graphics/icons/ne-spitter-land-mine-set.png

Mods to be disabled:
• Natural_Evolution_Enemies (0.18.1)

What version of Factorio? 0.18.28
Why does this happen? Factorio now uses 64x64 "HD" icons by default.

There might be something I'm not understanding here. If I am depending on another mod for a particular version, and I only have an old version installed, when does the game enforce the dependency version? I have tried removing and re-adding both mods multiple times and restarting the game.

Failed to load mods: The given sprite rectangle (left_top=0x0, right_bottom=64x64) is outside the actual sprite size (left_top=0x0, right_bottom=32x32).
If this is being used as an icon you may need to define the icon_size property.: Natural_Evolution_Enemies/graphics/icons/ne-spitter-land-mine-set.png

Mods to be disabled:
• Natural_Evolution_Enemies (0.18.1)

What version of Factorio? 0.18.28
Why does this happen? Factorio now uses 64x64 "HD" icons by default.

The icon is not from Factorio, but from NE Enemies. Icon size was changed to 64x64 in NE Enemies 0.18.3, prior to version 0.18.1 still had the 32x32 icons. So, if your mod used the icon from NE Enemies, but set "icon_size = 64", this would result in an error.

There might be something I'm not understanding here. If I am depending on another mod for a particular version, and I only have an old version installed, when does the game enforce the dependency version? I have tried removing and re-adding both mods multiple times and restarting the game.

Not sure I understand correctly. Would you mind posting the dependency you've set?