The number in the Aperture line of the Show Info for photos is the Aperture Value, not the F-stop number, even though the number is preceded by "F/" which implies it is the F-stop number. A photo taken at F/8 is has an Aperture of F/6 shown, and a photo taken at F/11 has an Aperture of F/7 shown. This is not a major problem but it is confusing when looking in PhotoScan to see what F-stop was used for a photo.
"Aperture Value" = log("F-stop") / log(sqrt2)
"F-stop = (sqrt 2) ^ "Aperture Value"
My understanding (perhaps incorrect) is the raw EXIF data contains the Aperture Value rather than F-stop. Most software converts it to the corresponding F-stop value before reporting.