Presumably to generate a unique name, valac generates C preprocessor defines such as . ___HOME_FAB_CD2_CAIRO_DOCK_PLUG_INS_DBUS_INTERFACES_VALA_SRC_CDAPPLET_H__ . ... which contain the build path.
Our notes about issues affecting packages are stored in notes.git and are targeted at packages in Debian in 'unstable/amd64' (unless they say otherwise).