Thanks trexx for the clarifications and the greater detail of your experience. I find it very interesting the myriad ways that inaminate objects have of perversely injecting anomalies into our best efforts!
Based on trexx's posts and Simon's post, I would say that the pinhole issue is the leading suspect currently.
Ok, then there is a mechanism which can produce localized excessive exposure when using a pinhole? And rather than over development this may be a case of exposure anomolies?
Assuming this is in keeping with Simon's finding, can anyone explain the phenomena in a way that we can exploit it or avoid it?