So you are saying that a secondary effect of a spell that can only target creatures which affects objects, allows the spell to bypass the
targetting restriction that prevents it from affecting Constructs and Undead in the first place?
Excuse me?
So in the Seething Eyebane example:
Target: Creature Touched
Duration: Instantaneous
Saving Throw: Fortitude negates (see text)
It blinds one creature, and causes 1d6 of acid damage to everyone within 5 feet. That can, in turn, damage objects (presumably "affecting them"). However, the spell cannot
target objects, nor does it have any affect when cast
upon an object.
Which is the basic question: if you cast Polymorph Other (or any spell with a Fortitude Save) on an object, does anything happen?
If the answer is
no, then whatever may or may not happen to objects after you target a creature is irrelevent: the spell does not affect objects
when cast upon them. That's the question, and when confronted with the Polymorph Other spell the answer is simply that nothing happens.
Target: One creature
Duration: Permanent
Saving Throw: Fortitude negates
That's all you have to read to see whether it "affects objects". It can't even target an object, and therefore cannot be cast upon them. Since you can't cast it on an object, it can't affect an object when cast upon them.
-Frank