Perpetual Polymorph Adept?

[Taja the Barbarian]

How are these two feats supposed to interact?

Perpetual Polymorph wrote:

Source Interstellar Species pg. 87

By assuming the form of a less powerful creature, you can dramatically extend the duration of your transformations.

Prerequisites: You know the polymorph spell as a 2nd-level spell or higher.

Benefit: When you cast polymorph on yourself and choose to transform into a predetermined polymorph form from a lower-level list of forms you know, you increase the spell’s duration. If you transform into a form that’s from a list one level lower, the duration increases to 5 minutes/level (D). If you transform into a form that’s from a list two levels lower, the duration increases to 1 hour/level (D). If you transform into a form that’s from a list three levels lower, the spell’s duration lasts until the next time you regain spell slots.

Polymorph Adept wrote:

Source Alien Archive 2 pg. 145

You are adept at changing forms using polymorph.

Prerequisites: You know the polymorph spell as a 3rd-level spell or higher.

Benefit: While your polymorph spell targeting yourself lasts, as a standard action, you can change into another form you know from that level of the spell or any lower-level version. This does not affect the duration of the spell.

If I cast Polymorph (IV) but select one of my Polymorph (I) forms, the spell duration is set to 'until I regain spell slots' which is straightforward enough. Now, what happens to the duration if the very next round I use the 'Adapt' ability to shift to one of my Polymorph (IV) forms? The 'Perpetual' feat seems to indicate the duration is set when you cast the spell (logically enough) and per the 'Adapt' feat text, changing forms '...does not affect the duration of the spell' so technically speaking it should continue to last until I regain spells regardless of the form level but somehow I don't think they had Perpetual Polymorph in mind when they wrote this (since the 'Perpetual' feat was written 4 years later)...

If the spell duration does need to be adjusted, any ideas on how to handle this?

[Felix Cohen]

It seems to me like that is indeed the RAW, but probably not RAI.
My reading of the text suggests that you could use a 4th level spell slot to assume a 1st level form for the rest of the day, using perpetual polymorph. Then use a standard action on your following turn to take on a fourth level form without affecting the duration. This is because polymorph mentions a form you know from the level of the spell, but not specifying that it needs to be one that the initial casting would have allowed.

However, my advice to the GM would be to only allow you to change into forms that your initial casting would have allowed you to take. Which would mean that if you cast 4th level polymorph to take a 1st level form for the rest of the day, you could only transform into other 1st level forms. It might be argued that this is intended if you believe that "from that level of the spell" in polymorph adept refers to the level of the form instead of the spell slot used.
Alternatively they could rule that the duration can decrease if you take a higher level form, but not increase when taking lower level forms.