object_parallel_to_source + linux + qmake

Hi,
I have strange QMake warnings

when I use:

CONFIG += object_parallel_to_source

I have got a lot of messages only on linux builds:

"QDir::mkpath: Empty or null file name
WARNING: Cannot create directory ''
QDir::mkpath: Empty or null file name
WARNING: Cannot create directory ''
QDir::mkpath: Empty or null file name
WARNING: Cannot create directory ''
....
QDir::mkpath: Empty or null file name
WARNING: Cannot create directory ''
QDir::mkpath: Empty or null file name
WARNING: Cannot create directory ''

My *.pri files looks like:

HEADERS += $$PWD/task.h
SOURCES += $$PWD/task.cpp

Everything else works correctly but tons of warnings masks in console important data (screenshot is attached).