Thankyou P Boyall, that sounds like the answer to what my instructor was referring to when he said that there were "Grey areas" wrt PFLs and Rule 5.
I think my instructor may also have been referring to whether PFLs do or do not come into "Normal Aviation Practice". Logic would have told me that they did......
Anyway, i'll know more when I've flown some PFLs with him....
GQ