qmake, qtconf with relative path

Setting relative path '..' in qt.conf does not work:

qt.conf:
[Paths]
Prefix=..

qmake -query shows wrong paths.

The releavant code is in qlibraryinfo.cpp, line 433
the variable ret with value '..' is ignored:

#ifdef BOOSTSTRAPPING
return QFileInfo(qmake_libraryInfoFile()).absolutePath();
#else