Why does Qt add 'PWD' to libraries that are NOT referenced relatively?

Question

Whenever I add a library in the .pro file of a Qt project (in Qt 5.2) it adds a $$PWD before the path of the libraries and include path. For example

INCLUDEPATH += $$PWD/C:/opencv/opencv-msvc2013/install/include

and

win32:CONFIG(release, debug|release): LIBS += -L$$PWD/C:/opencv/opencv-msvc2013/install/x64/vc12/lib/

My question is

1. why does Qt start the path with the PWD (Present Working Directory) keyword if its providing an absolute path to the libraries? What logic/good programming practice is this convention following?
2. And most importantly why it does not result in an error? How does Qt know when to search relative to a working directory and when not to? (Since both cases start with the PWD keyword)

PS : I removed the $$PWD keywords and my code worked just fine as well.

Answer 1

In case both the project and the library are in the same drive, that would not happen and the relative path is generated automatically. But on Windows if you add a library which is in another drive, it would add $$PWD followed by an absolute path.

This sounds like a bug and it has been reported here but it's still unresolved.