I think this is the norm - First Class leading southbound (and trailing northbound). On normal diagrams the HSTs▸ don't reverse en route and so are mostly the 'correct way round'. Weekend engineering work may sometimes cause then to be reversed, but I struggle to think of any diversionary routes that require a reversal - even going via Gloucester, Newport and then Parkway puts the sets 'right' way from Bristol Parkway southwards. Via Leicester, via Lichfield, via Doncaster instead of Leeds, via Worcester (going direct via Bromsgrove or via Smethwick West and Stourbridge), even via Westbury doesn't reverse the train. Remember the HSTs only run Glasgow / Dundee / Edinburgh via Birmingham NS to Paignton / Plymouth / Penzance and not to the South Coast. In BR▸ days allmost all HSTs reversed at Gloucester meaning First was at the correct end (southern end) north of Gloucester, and eastern end south of Gloucester thus matching the same locations on platforms as GW▸ InterCity trains and East Coast InterCity trains.
If a set enters service in reverse it's generally kept that way for the whole diagram to save any associated delays en-route, particularly if the empty stock movement at the end of the day can be used to turn them, a few routes that spring to mind where a train may turn for engineering / train fault reasons on the route are:
Motherwell (via Mossend and Holytown), Edinburgh Suburban line, Newcastle High Level Bridge, York to Leeds via Castleford, Sheffield to Chesterfield via Beighton, Chesterfield to Derby via the Erewash Valley, Birmingham to King's Norton via Camp Hill, Gloucester to Bristol via the tunnel (calling Filton vice Parkway).
Not an exhaustive list, but ones I can think of that
XC▸ drivers sign, there are few more north of the border but they's need route conducting.
