I first noticed this a few days ago on the Euston - Milton Keynes DLC and again on SEHS, where having set the PIS to the terminating station, the matrix display on the front and side of the train (if it has such a board) reads "Not in Service". With SEHS, on the side of the 375, it listed off all the stations and ended with "...Bromley South and Not in Service". I haven't played any other route so far to see if its affecting the names of all terminating stops or not. - "...Bromley South and Not in Service".
I haven't tested it on London Commuter as its hard to get the motivation to play TSW much anymore, but it not an issue on East Coastway.