Qt 4.8.x is highly recommended.

If header (h) or interface (ui) files have changed, please perform
a distclean before building Dooble.

Absolute cleaning:
make distclean or mingw32-make distclean

OS X:
qmake -spec macx-g++ -o Makefile dooble.osx.pro
make

Unix:
qmake -o Makefile dooble.pro
make

Windows:
qmake -o Makefile dooble.win.pro
make or mingw32-make
