Tile improvement not changing underlying terrain when given as a gift

[SpacedOutChicken]

Is there an existing issue for this?

• I have searched the existing issues

Game Version

4.18.2

Describe the bug

If a tile improvement that has the "Turn this tile into a [terrainName] tile" unique is given as a gift to a city-state, the tile beneath the new improvement will not be turned into anything new.

Steps to Reproduce

1. Create a tile improvement that improves a strategic or luxury resource and that has the "Turn this tile into a [terrainName] tile" unique
2. Gift that improvement to a city-state
3. The underlying tile will remain unchanged

Screenshots

Here's the before shot:

Here's the after shot, with the improvement built but the tile underneath still a Lava tile instead of a Crust tile:

Link to save file

Here is the saved game, with a Magnesium resource tile in Arasta's territory waiting to have a Crust platform built on top of it.

Before gifting improvement.json

Here is the mod that I'm developing that this saved game uses:

Rivers of Lava.zip

Operating System

Linux

Additional Information

No response