Relative includes (*.pri) don't work when project is open with -client option when path contans native separators on windows

Suppose we have project and subproject with this file structure

D:\project\config.pri
D:\project\project.pro
D:\project\subproject\subproject.pro

And subproject.pro contains relative include

include(../config.pri)

or

include($$PWD/../config.pri)

Opening subproject in one of this ways works well

qtcreator D:\project\subproject\subproject.pro
qtcreator D:/project/subproject/subproject.pro
qtcreator -client D:/project/subproject/subproject.pro
cd D:\project\subproject && qtcreator -client subproject.pro

Everything works and looks nice

However when you try to open like this

qtcreator -client D:\project\subproject\subproject.pro

QtCreator shows fullpath instead of basename and doesn't show include since it cannot locate it

and cannot build project due to "missing" config.pri (error shows that path to include computed incorrectly)

Debug output shows that QmakeProject() constructor recieves path with native separators but expects unix separators because Utils::FilePath relies on that. I cannot track full path it makes before ending up unclean only in later case, but I can suggest fixing it somewhere along the way, for example in ProjectExplorerPlugin::extensionsInitialized (patch in attachement) or in ProjectExplorerPlugin::openProject or in ProjectExplorerPlugin::openProjects