This question is two-fold. The main part of it is a rules question (I accept RAW and RAI, btw, based on which makes the most sense and balance).
A player of mine was reading the Combined Spells portion of MT, and wondered if, by preparing a wizard's spell in your cleric slot:
1. Do these spells still suffer ASF?
2. Is the spell arcane or divine when cast in this way?
3. Can these spells be spontaneously converted into Cure spells?
The other part of the question, my own, is: even if the above aren't RAW, would you feel allowing them would be OP in a game that isn't minmax/OP'd, but was more towards the middle?
Anyway, I would appreciate your help.
Here's the text of the ability, as per the PRD:
Combined Spells (Su): A mystic theurge can prepare and cast spells from one of his spellcasting classes using the available slots from any of his other spellcasting classes. Spells prepared or cast in this way take up a slot one level higher than they originally occupied. This ability cannot be used to cast a spell at a lower level if that spell exists on both spell lists. At 1st level, a mystic theurge can prepare 1st-level spells from one of his spellcasting classes using the 2nd-level slots of the other spellcasting class. Every two levels thereafter, the level of spells that can be cast in this way increases by one, to a maximum of 5th-level spells at 9th level (these spells would take up 6th-level spell slots). The components of these spells do not change, but they otherwise follow the rules for the spellcasting class used to cast the spell.
Spontaneous spellcasters can only select spells that they have prepared that day using non-spontaneous classes for this ability, even if the spells have already been cast. For example, a cleric/sorcerer/mystic theurge can use this ability to spontaneously cast a bless spell using a 2nd-level sorcerer spell slot, if the character had a prepared bless spell using a 1st-level cleric spell slot, even if that spell had already been cast that day.