--diff-filter=T does not list x changes

From documentation, I would expect --diff-filter to list changes in

the execute bit, but it does not. I hear on #git that this is
intended, though I still do not know how to filter on the execute bit.
Is it impossible?


Testcase:

  mkdir t && cd t && git init
  touch a && git add -A && git commit -m1
  chmod +x a && git add -A && git commit -m2
  git log --diff-filter=T        # <--- shows nothing
  rm -f a && ln -s b a && git add -A && git commit -m3
  git log --diff-filter=T


Anders