Can't build for UWP after having built for Desktop

1. Have a checkout of qtbase.
2. In this checkout, run git clean -dxfn to make sure that there are no files which are not checked in to the repository.
3. Have two kits set up in Creator, one for the Windows Desktop and one for UWP.
4. Open a project from the repository in Creator.
   I used the shortcuts test in tests\manual\shortcuts\shortcuts.pro
5. Configure the project to use both kits.
6. Make the Desktop kit active.
7. Select "Build" -> "Run qmake" from the menu.
   In the "Compile Output" view, you can read something like:

   Info: creating stash file D:\dev\src\qtbase\.qmake.stash
   

   This seems pretty wrong already.

8. Make the UWP kit active.
9. Select "Build" -> "Build All Projects" from the menu.
   Building will fail. In the "Compile Output" view, you can read something like:

   Der Befehl "cl" ist entweder falsch geschrieben oder
   konnte nicht gefunden werden.
   jom: D:\dev\src\qtbase\tests\manual\build-shortcuts-Qt_5_15_0_for_UWP_64bit_MSVC_2015-Debug\Makefile.Debug [.obj\debug\main.obj] Error 1
   jom: D:\dev\src\qtbase\tests\manual\build-shortcuts-Qt_5_15_0_for_UWP_64bit_MSVC_2015-Debug\Makefile [debug] Error 2
   20:33:03: The process "C:\Qt-05.06e\Tools\QtCreator\bin\jom.exe" exited with code 2.
   Error while building/deploying project shortcuts (kit: Qt 5.15.0 for UWP 64bit (MSVC 2015))
   When executing step "Make"
   

10. Delete the file .qmake.stash which Creator created.
11. Select "Build" -> "Build All Projects" from the menu.
    Building succeeds.

Looks like Creator writes .qmake.stash to the wrong place. If this really is the right place, Creator will have to remove the file when switching kits.