Project file not using tabs when adding files to sources and headers

When adding files to a project they are automatically added to SOURCES and HEADERS of the .pro file as expected, but even if the "Tabs And Indentation" policy of Text Editor and C++ is set to "Tabs Only" the indentation is done with spaces.

Manually saving the .pro file replaces the spaces with tabs as expected, but if you don't do that the .pro file will keep the spaces when closing Qt Creator.

Steps to reproduce:

• Create a new project
• set all "Tabs and Indentation" policies to "Tabs Only"
• Add a new class to the project

Result:

The .cpp and .h files are added to SOURCES and HEADERS variables, but spaces are used for indentation.

Expected result:

The .cpp and .h files are added to SOURCES and HEADERS variables and tabs are used for indentation.