1. Create/Import a generic project (e.g. a previously created Qt Gui Application)
2. Open mainwindow.h and put the cursor on the declaration of the constructor.
3. Hit F2 to go to the definition in mainwindow.cpp - that works.
4. Close mainwindow.cpp
5. Add a file to the generic project
6. Hit again F2 on the constructor declaration - nothing happens. The generated output is "undefined document: /home/nikolai/dev/creator/qtcreator-2.8-debug-build-qt5/bin/untitled/mainwindow.h"

This is a regression from 2.7

The underlying problem is that the GenericProject calls updateSourceFiles() only with the added files instead of all files (as e.g. the Qt4Project does).