While shooting stills in JPEG+RAW on my P3P I recently noticed an ever so slight arcing of the horizon in RAW but not in the JPEG. Have any of you noticed the same?

I have the P3S but only shoot RAW so would not notice any difference.

The RAW file is the data set from the sensor without any processing. The Jpeg has processing applied. If what you say is correct then there must be some lens distortion correction in the processing.

Some software graphics programs have lens "profiles" for the Phantom models.  These correct for the lens.

This would be because whatever program you are using to view the RAW image is not applying a lens profile. There is some spherical aberration in the lens, and it is normally corrected in the camera when shooting JPEG.

Thanks for the info on lense profile. I am viewing with Photoshop Elements 11 which I have had for a few years.