I have found what seems to be a contradiction in how the 5th level spell Cloudkill affects creatures of certain HD:
These vapors automatically kill any living creature with 3 or fewer HD (no save). A living creature with 4 to 6 HD is slain unless it succeeds on a Fortitude save (in which case it takes 1d4 points of Constitution damage on your turn each round while in the cloud).
A living creature with 6 or more HD takes 1d4 points of Constitution damage on your turn each round while in the cloud (a successful Fortitude save halves this damage). Holding one's breath doesn't help, but creatures immune to poison are unaffected by the spell.
So for a creature that has 6HD, it is simultaneously under two contrary conditions, either save to stop a death-effect and only take 1d4 constitution damage or only ever get 1d4 con damage and a fortitude save to halve the result of that.
There doesn't seem to be any errata on this despite it being in the core rulebook.
Do I have to houserule a solution or is there an objective ruling on how to deal with such a contradiction?