Can build some improvements but not others?

[seebs]

This is so weird. I have a saved game with a worker standing on a hill-with-sheep.

If he tries to build a pasture, the game crashes instantly. If he tries to build a mine, it works.

I have a nearby grassland tile where I can build roads, but not a house, and another grassland+sheep where I can build roads, but not a pasture.

WTF?

[seebs]

I just realized:

This is one of the reasons games crash while the computer is running automated workers. Because they trigger bugs. I just verified that, if I click on "automatically build a trade network", my worker crashes the game by trying to perform a forbidden action.

[seebs]

I think I found it. With all the logs on, I get a warning about being "unable to place" a tile in the LSystem log. That's the log file for the system used to draw things like, say, improvements. So it would make sense that it would crash the game if it couldn't find a way to draw a given improvement...