Here are two examples:
A) Extend Spell and Persistent Spell are applied to Divine Favor. Is the Extend Spell feat or the Persistent Spell feat applied first? If Extend is applied first, the duration is doubled, then changed to 24 hours. If Persistent Spell is applied first, the duration is made 24 hours then doubled for a result of 48 hours. Does the caster get to choose the order in which the feats are applied to the spell?
B) How is a twined, empowered, split ray of enfeeblement handled? (targeting one creature)
1) Is it ((((1d6+5)*1.5)*2)*2)? Empower is applied first, then the spell is split into two rays, then twinned. This is the most beneficial to the caster. It is possibly overpowering as it results in a penalty of 36-64 to the targets strength.
2) Is it (((1d6+5)*1.5)*3)? This is like the above example, but uses the rule on multiplying when doubling a double.
3) Something else?
Some say metamagic feats are applied only to the base spell, but this results in nonsensical occurrences such as an Extended Energy Substituted (Cold) Maximized Acid Arrow? If the feats don't interact at all it'd have to deal a combination of Maximized([cold + acid]) for the original duration the Rolled([acid]) for the Extended portion. Plus there is only one mention of feats not interacting, and that is the example under the Maximize Spell feat.
I have used the following rule:
The caster may designate the order in which metamagic feats are applied and choose the most beneficial application of those feats, unless the feat makes note of an exception.
