My best guess is git tf pull --rebase adds a trailing unix line ending when the file does not have a trailing end-of-line and another user had modified the file causing a merge.
This problem occured again, this time on a .csproj file:
1. changed .csproj file
2. git add -A, git commit
3. no unix line endings in my working folder
4. git tf pull --rebase
5. since my last pull another user modified the same .csproj file, git merged the changes automatically (did not need to use git mergetool)
6. after this command completed, I found a unit line ending