Ignoring whitespaces on diff does not work

Expected behavior

When I call:

  var options =
                new CompareOptions()
                {
                    ContextLines = Int32.MaxValue,
                    IncludeUnmodified = true,
                    Similarity =
                        new SimilarityOptions()
                        {
                            WhitespaceMode = WhitespaceMode.IgnoreAllWhitespace
                        }
                };

Console.Write(
   repo.Diff.Compare<Patch>(
      branch.Tip.Tree, 
      DiffTargets.Index | DiffTargets.WorkingDirectory, 
      files,
      null,
      options
   ).First().Patch
)

the output is the same as using the git command git diff --ignore-all-space:

diff --git a/test.txt b/test.txt
index d209983..b2c9980 100644
--- a/test.txt
+++ b/test.txt
@@ -1,2 +1,2 @@
 I am an  initial  content
-I am a changeable content
\ No newline at end of file
+I am a different content
\ No newline at end of file

Actual behavior

If have a file "test.txt" with committed content:

I am an inital content
I am a changeable content

and uncommitted content:

I am an  inital  content
I am a different content

(The first line has some additional whitespaces)

When I call:

  var options =
                new CompareOptions()
                {
                    ContextLines = Int32.MaxValue,
                    IncludeUnmodified = true,
                    Similarity =
                        new SimilarityOptions()
                        {
                            WhitespaceMode = WhitespaceMode.IgnoreAllWhitespace
                        }
                };

Console.Write(
   repo.Diff.Compare<Patch>(
      branch.Tip.Tree, 
      DiffTargets.Index | DiffTargets.WorkingDirectory, 
      files,
      null,
      options
   ).First().Patch
)

the output is

diff --git a/test.txt b/test.txt
index d209983..b2c9980 100644
--- a/test.txt
+++ b/test.txt
@@ -1,2 +1,2 @@
-I am an initial content
-I am a changeable content
\ No newline at end of file
+I am an  initial  content
+I am a different content
\ No newline at end of file

Version of LibGit2Sharp (release number or SHA1)

v0.26.2

Operating system(s) tested; .NET runtime tested

Start by reproducing the Compare example with CompareOptions, SimilarityOptions, and WhitespaceMode.IgnoreAllWhitespace, then compare its output with git diff --ignore-all-space. Trace the diff comparison path that handles whitespace modes. Done means whitespace-only changes are ignored while substantive changes still appear in the patch.