How to reproduce:

1. Create appropriate Kit for (Qt 4.8.6 && MinGW)
2. Open the qbs example: \qbs\examples\app-and-lib\app_and_lib.qbs
3. Ensure that are used desired Kit.
4. Select in project three an "application" or "library" item (any sub-product)
5. Click on right mouse button to show context menu
6. Select "build" project option
7. Watch for forever freeze of QtCreator

In "Compile output" window are displays only:

12:51:13: Running steps for project app_and_lib...

The QtCreator can be terminated/killed only from the Task Manager.

Clicking on "build" or "rebuild" option of a root item does not lead to freeze, so build completed successfully.

This reproduced on Qt4 using MinGW or MSVC2010 compilers. But with Qt5 are not tested.