Terrforming new rivers

[Theben]

I've discovered a bug new to me. If I terraform tundra squares the square becomes 'coal, river' (i.e. there is no base terrain per se). The next turn if I irrigate it or mine it becomes 'desert, river'. After that point it's treated as a standard desert tile with a river in it. Anyone had this occur before?

I should mention that it's a modded version of 2.78.

[Henrik]

Not new , happens whenever you transform a terrain with no terrain given in case of transform.
You've set tundra to be untransformable right?

If one wants to avoid transformation of terrain it's better to set the terrain to transform back into itself. The only terrain which can have transform set to "no" is ocean.

[Mercator]

Yep, this dates back to the days of Glyphweb. See this thread in the hints, tips and guides subforum:

http://apolyton.net/forums/showthread.php?s=&threadid=66105

[Theben]

Originally posted by Henrik
Not new , happens whenever you transform a terrain with no terrain given in case of transform.
You've set tundra to be untransformable right?

If one wants to avoid transformation of terrain it's better to set the terrain to transform back into itself. The only terrain which can have transform set to "no" is ocean.

Yep. It's untransformable. Just thought I'd check though.