Unable to switch from .h to .c file with Switch Header/Source in some situations

Attempting to use Switch Header/Source from a .h file to a corresponding .c file fails in the following situation:

• A project is a mix of .c and .cpp files.
• The header and source are in different folders.
• The source file is a .c file.

To reproduce:

1. Download test.tar.gz and open in Qt Creator.
2. Open src/TestFile.c
3. Invoke Switch Header/Source, the editor will switch to include/TestFile.h.
4. Invoke Switch Header/Source again, the editor will NOT switch back to src/TestFile.c.

Functionality will be restored if:

1. Main.cpp is changed to Main.c, making "test" a C-only project.
2. include/TestFile.h is moved to the src directory, so the .c and .h files are in the same directory.
3. TestFile.c is changed to TestFile.cpp.