QMake fails to generate correct Makefiles when following conditions apply: unix, shadowdir build, .pro file, .pri file refers to a file with case error in file name

QMake fails to generate correct Makefiles when certain conditions apply.
Conditions:

• unix, generating a Makefile
• case sensitive filesystem
• shadowdir build, (e.g. out-of-source tree build)
• .pro file which includes a .pri file
• .pri file refers to an existing file, which case error in filename
• files are referred with $$PWD

The generated Makefile is otherwise correct, but the filename to which was referred incorrectly has one extra ../