To reproduce this problem, take these steps

1. take visual studio binary package of qt
2. go to the examples/analogclock (or other example)
3. delete files manually (except source and .pro files)
4. try building the example using mingw version of qt inside the original directory
5. results are a lot of undefined references (see attached picture)

Solution: If you copy the example first to another directory, it builds fine.

If this is an expected behaviour of qmake, it should be documented.