I’m getting a breaking crash (spin lock) using the terrain brush (macOS 10.15). In the project below try to use the terrain brush on the layer “Main” with the “Mountain Base” set and after a few attempts it should get stuck in an infinite loop. Let me know if it can be reproduced.
I’ve been playing around for a while with “Mountain Base” and clicking around on the “main” layer, but I couldn’t get it to crash. I’ve tested both with latest development version as well as Tiled 1.2.1 which I happened to have installed.
Which version do you have installed, and do you think you could make the instructions a little more precise?
Unrelated to this, I don’t think what you’re trying to do will really work nicely, because the terrain tool has too little information to place the “Mountain Base” tiles correctly.