I am assuming you are referring to the 12:44 Newcastle to York and the 14:07 York to Newcastle. It was introduced in the last change to the temporary timetable to facilitate the extension of a couple of the Scarborough services to/from Liverpool during the day (rather than just the peak time services) using 68/MK5 stock.
The 12:34 SCA-LIV runs in the path of the Newcastle between York and Liverpool with the subsequent 12:44 ex Newcastle service terminating at York. This is to maintain a 30 minute frequency from York towards Manchester.
That train then picks up the normal Newcastle path back north at 14:07, with a Scarborough service running the 11:54 departure from Liverpool (minus the layover at Manchester Victoria so it can run in the Scarborough path), but still allows a 10 minute connection at York for Newcastle passengers.
Aside from that train, there is a late night service that terminates at York to form ECS to Doncaster for maintenance. Similarly some early trains start at York and head for Newcastle as the stock comes from Doncaster.