I have a project with a dynamic library an a application. The application depends on the library, if I change a header file in the library and build, qbs don't rebuild the library.
I don't know if this is a general qbs problem or a problem of the QtCreator integration (I only testet it with the Creator, Version 3.1.0)

I figured out how this can be reproduced. I missed to report one important information. The library has a extra directory with header files, this directory contains headers for applications using this library. The headers only includes the "real" library headers, like the Qt headers (e.g. the QtCore header) includes the "real" headers. This directory is set as includePath in the QBS file.
The library uses this headers too, so the library .cpp includes the headers indirectly. The "real" headers are in the QBS file, but QBS seems ignore them because they are not directly included (the header files in the include path are NOT in the QBS file).

I attached a example. If you change the header in the library, you will see that the library is not rebuild.