Indeed, for some reason with the ATW 158 PIS, it doesn't list the next (mandatory) stop. It happens at every stop as I saw when I was travelling back from Pwllheli earlier in the week, but it wasn't out of sync. E.g. upon leaving Welshpool it said the next stop would be Shrewsbury, but then, shortly after this, a scrolling list of stations appeared saying "Calling at Wellington, Telford Central..." etc.
I actually think the way it deals with request stops is acceptable due to the uncertainty of where the train will stop. I.e. At Penrhyndeudraeth it says something like "We are now at Penrhyndeudraeth. The next stop is Harlech. If you wish to alight at Llandecwyn, Talsarnau or Tygwyn, please ensure you tell the conductor." I do have a recording somewhere, I'll see if I can find out how to upload it.
I imagine it's difficult to code request stops as it seems to update with the doors being released so it would easily get lost not stopping at stations, and I think ATW opted for the best option, even if request stops only get announced after leaving the last mandatory stop before. The guard will often make announcements for stops that have been requested by passengers on the train anyway, advising them about low level platforms, or where to alight.
From what I've seen on trains running to Weymouth, the GWR PIS just unhelpfully completely ignores the request stops. It also gets confused when extra carriages join for strengthening or if the local door only is used. Slightly concerning when these 150/2s are going to be operating on lines where these are likely to continue to happen.
