John, thanks for the info, much appriciated.
PTgui 9.1.2 works great, no more errors with VP correction + faster then previous versions.
Below a 100% crop comparison of the nadir (of equirectangulars) of a hand held pole pano without and with VP correction (after run 1 VP correction was switched on, then optimized with the same CP's and output as run 2 ).
The relatively small improvement of just 20% less CP errors by using VP correction is obviously enough to help to get a better result with Smartblend (my prefered blender for handheld pole panos).
I see this improvement often, hence my use of VP correction for handheld pole panos.