Michael Lowry said:
This should probably be documented.
Or, in frankness, changed. Because symlinks are supposed to be handled transparently, and one can follow a symlink for writing, I personally don't see a good reason for UC4 handling it this way. I suspect UC4 removes or even unlinks the file, then rewrites it from scratch. Which, if so, would also leave you with no file at all if something goes wrong in between.