was a recalcitrant Synaptics touchpad v clickpad driver clash. This is not a new issue and has dogged HP laptops (and other manufacturers I believe) since windows 8.0. Essentially every new Windows update/release identifies the touchpad as a clickpad and installs the driver assigning the most used gestures to fixed functions. I use the three finger left and right swipe to go back and forth on webpages etc and this effing driver uses it to alt tab. I have to disable the driver update in the group policy editor. 4 machines and this is the only issue so far, fingers crossed.