We've had people get into trouble because of Trainline split tickets where one of the part journeys has been fulfilled with an Advance ticket, and the purchaser had not realised that they were bound by the train times given.
At least it's not as bad as Chiltern and Grand Central, whose booking sites sell split tickets without indicating they're doing so, and double down by only showing the ticket name for the least restrictive ticket involved. So you only find out about it at the fulfilment stage, when you get two separate tickets! It does generate separate barcodes for each actual ticket, but incorporates the full itinerary on each, rather than just the part that applies to that particular leg.
For example:
https://buy.chilternrailways.co.uk/...dren=0&railcards=[]&ls=LS_1_2&p=PRICE_P_1_117
The above is a search for a journey from York to Cross Gates, departing on 7th November after 10:30. The Anytime Day Single for the through journey is £18.60, but one of the options it's showing me at the time of writing is described as an Anytime Day Single but priced at £8.90. The only hint that something's not quite right is when you click through to buy it and it gives a "You must reserve a seat with this ticket" message.
For bonus points, it also uses IATA codes for stations in the search URL, where they exist, and throws an error if you try to change it to the CRS code!