Weird random culture yield on tile

[Acratenn]

Just started a new game, went out exploring, and located this gem of a tile in the attachment.

 

[lukeloh]

v154.0 - I have seen the same, but on a plain Grassland tile. Now in Renaissance, and no Resource has spawned on that tile. So it appears to be a bonus directly related to the tile itself.

 

[Thalassicus]

I've noticed the same thing occasionally for a few weeks now. I'm not sure where it's coming from. I've searched a few likely sources without locating the bug yet.

 

[Sanguinus]

Could it be a natural wonder that is not drawn or processed correctly?

In vanilla there is only Fuji-san with +6 .

 

[Thalassicus]

I don't know. It's happened too rarely to identify a pattern yet, and I didn't see any obvious mistakes in code dealing with culture.