Erroneous "diff --summarize" output?

I just noticed some strange output from diff --summarize that to me looks like a bug, but I'm not sure.
What I'm doing is that I'm changing a file in a subdirectory, committing it and then reverse-merging that change so I'm back to the same content of my working copy as before. Running svn diff against the previous revision shows no diffs as expected, but when I do the exact same command but add --summarize, it says the file that I changed is modified and the directory it is in has property changes.
The attached reproduction script illustrates the difference. Is this a bug or am I misunderstanding how summarize is supposed to work?

BR,
  Chris