Stashed files reappearing in "unstaged" section of sourcetree (and in git status output)

Question

In Sourcetree (3.4.10) if I stash my current folder, the files that were modified pops back again in my "unstaged" area.

this even though I havn't selected the flag "keep staged modifications".

git version is 2.37.0 on Windows10

Also if I

$ git status  
Changes not staged for commit:
     modified: myfile.cpp
$ git stash  
$ git status  
Changes not staged for commit:
     modified: myfile.cpp
$ 

I find the list of modified files that in my ideas should have been stashed

EDIT:

also p4merge (called from sourcetree) says:

0 diffs (Recognize line endings and whitespaces differences), tab spacing: 4, encoding: UTF8, No BOM