Focus Shift: 50mm f/1.8G

The 50mm f/1.8G was Nikon's update to their cost effective 'D' and initial reviews where favourable. However, after using this lens for a number of years now I was still having issues with misfocus at wider apertures on my Nikon bodies. This behaviour was consistent across 2 other 50mm f/1.8Gs too but recently someone pointed out an optical phenomenon called focus shift that may be a potential cause...