Sometimes the package need other with specific use flag. However it is unpleasent if you start compilation at night and you wake up in the morning only to be informed that the second package from 100 has crashed only because the first package was build without specific flag.
1. Put it into special varieble in order to show on the begining what is wrong (during dependecy calculation, 'crashes' due to package masks etc.) - personally I prefere this one
2. Auto-rebuild required package
*** This bug has been marked as a duplicate of bug 2272 ***