[win32] qt places built libraries in wrong directory

For example, I build Qt-4.8.1 in C:\qt\qtbuild with following commands:
configure.exe -debug-and-release -opensource -platform win32-g++-4.6 -prefix C:\Qt\4.8.1
mingw32-make

Everything built goes into C:\qt\qtbuild (i.e. ${BUILD_DIR}), except for qt libs, QtCore.dll and else, they go into C:\Qt\4.8.1\bin (i.e. ${PREFIX}\bin). I think this is incorrect behavior. Also not tested how this would interact with following command:
mingw32-make install
without INSTALL_ROOT defined.