I'm looking at this now. I'll see if there's some way we can improve this soon.
At the moment, project files with these characters won't load properly, but it should then give you an error. If you see the "Parse error: not well-formed (invalid token)" error, don't save the project afterwards. I have never seen TG3 or TG4 corrupt the project at save time, unless it's already loaded incorrectly. So I think what happened is that you loaded the project and the error message was hidden from you somehow (the Errors and Warnings window doesn't always pop up at load time, I've noticed), so you didn't know there was a problem, and then you saved the corrupted project. Terragen needs to get better at preventing this from happening.