OK, I finally figured it out. Apparently on the Ubuntu kernel/filesystem chmod() on /proc/self/fd/ when it is a symlink will fail, while on my Fedora kernel/btrfs it succeeds (though has no effect). Let's simply skip the chmod() for symlinks since that has no effect anyway. That's what the new version I just force pushed does. That's the only change.

Since the change is so minimal to the earlier version that already was green-labelled, taking the liberty to green-label this one again.