QUOTE (Dakka Dakka @ Nov 30 2010, 02:43 AM)

Spirit+Vessel is different from both the spirit and the the vessel. As such spells don't carrya over. I'm not sure if they just don't give any benefits or if they are broken.
No, no and no
All spells affect the composite entity of Spirit+Vessel.
No.
While I can see the logic to your arguments, what you've basically just described is that a spirit possessing a vessel serves as an instant, unresisted, unstoppable counterspell to any and all spells affecting the vessel at the time of possession. Not only is that likely undesirable from a game balance perspective, but there's nothing in the rules or the fluff to suggest that such a major side effect would occur.
QUOTE
Welcome to Dumpshock
Thanks, but I've actually been here for quite a while

I suspect that the scenarios I've outlined above are simply situations that the author(s) didn't happen to think of, so there's no hard and fast RAW answer for how to handle them. I think that many of the posters have had some reasonable ideas for how one might house rule them, and I suspect that if and when such scenarios might pop up, having a chat with your GM about what makes sense for your own game is the best way to handle things.
My own impression, given both the flavor and the mechanics of the Possession rules, is that any spells currently affecting the vessel continue to affect it after possession begins, but only those which affect its body. The vessel's mind is, from all accounts, separate from the possessing spirit, and only able to watch helplessly at the events which transpire during the possession. Hence, any spells affecting the vessel's mind at the time of possession would
not carry over; Increase Logic/Control Thoughts/Control Emotion/Compel Truth/etc would still be 'active', they would just be affecting the vessel's (imprisoned) mind, not the spirit's. Any such spells cast
during the possession would, logically, affect the spirit, not the vessel, since it is the spirit whose mind is in control. It seems logical that you could cast something like Control Thoughts or use an adept power like Commanding Voice to force the possessing spirit to release the vessel, for instance. Likewise, if you've cast something like Increase Charisma on the spirit-possessed vessel, you're affecting the spirit's Charisma, not the vessel's; it makes sense that the spell would continue to affect the spirit after possession rather than transfer to the vessel.