Problem sorted! Not only that, but more good news is that the game does appear to respond fine with my xbox controller active (I do use keyboard concurrently too!). It was the Isolation Switch and preparation thereof of any trailing locos! Once the locos were set to RUN then panning the view around had no braking effect. If this was some kind of undocumented reminder for the engineer to check and prepare their consist, then it's a doozy. Now that I understand it, I love the idea of the game telling me that something isn't right when I pan the view to look back at the consist!
It is noted that the ES44 supplied with Montana Hi Line does not exhibit this behaviour, but that is probably because that route is not listed as a supported DLC...
Gentlemen, it is about this time that I humbly mumble the words, "Must RTFM!"
John, I thank you for the gentle reminder about one does not simply jump into a loco and go and your patience with this dumb limey (it took me a minute to locate the manual because I'd incorrectly assumed that the program was just a sound enhancement pack)
I have a further question regarding the train length function (SHIFT A, SHIFT D to cancel). I activated it when the nose of my loco passed the speed sign (going from 10 mph up to the 30mph section). Whilst the pop up told me the length of the train (more than a mile long!), it did so before the back of the train had passed the sign. In UK stock (Class 66 for example) the length of train seems to work right on the money (different script with an in cab button to press). When should the engineer activate this function IRL, as well as within the limits of TS?