I have tried searching for this, but have not seen it addressed. Each class that casts has metamagic action point enhancements such as improved empower, etc. Do these stack across classes? I really have no idea as in general passive enhancements tend to stack more than others, such as elven arcanum with class specific SP increases, but in the case of metamagic enhancements I have a feeling they may have intentionally kept that from happening.
If anyone knows this definitively, and lets me know, that would be wonderful.