Oh that's strange, you should only need to hold to use it, once you release it should be disabled.
Tried to recreate it, and I think it happens when:
1. hold the mouse inside the game
2. move the mouse out of the game without releasing the holding mouse
3. release the mouse outside of the game
4. move the mouse back inside and the terraforming ability is still triggered while the mouse is released.
I tried Windows, and it has no problem.