Whilst uncommon, this isn't the first time it's happened. the two classes are not allowed to run in service together, but can couple to rescue/run out of service. Does remind me of the time someone on depot would try to run a 387 in the middle of a 12 car move from one depot to another for wheel attention, and in putting it in the middle of the consist it was hoped the driver might not notice as whilst they are effectively the same train from a maintenance perspective, they are seperate on a drivers traction knowledge (a 387 is as similar to a 377 as each sub class of 377 is to eachother!)