GitFlow fails with --no-commit in .gitconfig

Followup from https://answers.atlassian.com/questions/170516/sourcetree-git-flow-hotfix-branch-merges-into-branch-develop-only:

Having the follow section within my .gitconfg-file:
-----------
[branch "master"]
mergeoptions = --no-commit
-----------

results in failure using gitflow (hotfix, release, feature).

What I did:

• Branch develop and branch master are on the same commit at the beginning
• Created a Hotfix Branch via git flow-Button (
  This happened on HEAD of branch "release" -> OK
  fixed on hotfix branch ....
• Finished hotfixing via git flow-Button ->
  a. Hotfix-Branch was deleted -> OK
  b. merge to branch "develop" took place -> OK
  c. switch to branch "develop" took place automatically (active branch is now "develop")
  d. merge to branch "master" took NOT place -> NOK (master is unmodified)
  e. Head of Branch 'master' is tagged with the provided tag (via git-flow dialog box)

What I expected according A successful Git branching model:

Hotfix has to be merged to branch develop as well as to branch master. Head of Branch "master" should carry the given Tag.

=> This does not happen within sourcetree: merge from branch hotfix to branch master does not take place automatically!!

I see the same behaviour with using Release-Branches via git-Flow Button within SourceTree: Starting point of creating branch "Release" is here HEAD of branch develop (that's correct for release branches).

Finishing the release branch only merges to branch develop - merge to branch "master" does not take place ...