I am in way over my head here (meaning I could be all wrong about this), but I just ran into massive problems because DirectFB got built (upgraded) AFTER libsdl instead of before. I assume that putting DirectFB into DEPEND instead of RDEPEND would fix this. The log file for libsdl does include numerous references to "-I/usr/include/directfb" so it seems that libsdl needs DirectFB there to compile (and not just to run).
*** This bug has been marked as a duplicate of 152405 ***