Ok, this one's a bit of a convoluted story as I came across it all trying to do a homebrew, PF converted version of a psionic mind flayer for my own use (it manifests psionics as a psion/telepath). Anyway, so examining the unbodied for inspiration, I was playing around with it/testing the PF Unbodied from Psionics Unleashed and found some issues.
The PF Unbodied has its own special casting class put into PCGen that won't stack with levels of psion at all (Psion's psionics start at level 1) does not get base power point progression nor spell selection when taking prestige classes (cerebremancer for example).
Okay, so I go back and look at the 3.5 version to see what it's like. It has the bonus PCLevel thing and stacks with psion levels, however when you take a level of psion the power points go through the roof. And if you take levels of a manifester level increasing Prestige Class without taking a level of psion, base power points do not improve. It would seem like there are some issues with power point progression and how it relates to effective manifester level.