Simple RAW Thread for 3.5 #35: 3/2 Score And Four Threads Ago

[lucmarin]

Q206

So the PrC Frost Mage has the feature "Gain Knowledge"

Gain Knowledge (Ex): Beginning at 3rd level, the frost mage gains knowledge of the spell conjure ice beast I, if he does not already have it. Former wizards get to add this spell to their spellbooks for free, and former sorcerers and bards get to add this spell to their spells known, even if this takes them over their normal limit. For each two levels gained in the prestige class, he gains knowledge of the next higher level in the conjure ice beast spell progression (conjure ice beast II at 5th level, conjure ice beast III at 7th level, and conjure ice beast IV at 9th level). At 7th level, in addition to gaining conjure ice beast III, the frost mage gains animate snow as a spell known. At 9th level, in addition to gaining conjure ice beast IV, the frost mage gains frostfell as a spell known.

This class feature does not change the level of the spell. A frost mage still must have a spell slot of the appropriate level to prepare or cast a spell acquired through the gain knowledge ability.

Conjure Ice Beast 1-4 and Animate Snow do not appear on the Sorcerer spell list, as such I assume it's safe to say that a Sorcerer taking levels in Frost Mage would, for example, learn Animate Snow as a 6th level arcane spell.

However, the spell Frostfell is both an 8th level Druid spell and a 9th level Sorcerer spell. Would a Sorcerer taking levels of Frost Mage learn it as an 8th or 9th level spell?

tldr:

If a prestige class would allow a spontaneous caster to learn a spell that appears on the spell lists for multiple classes (Frostfell), are you forced to learn it at the level that it uses on the spell list of the class whose spells known/spells per day are being advanced by the prestige class, or can you choose to learn it at the level a different class would?