A famous incident in the gospels is the feeding of the five thousand. Matthew and Mark both say this occurred in a "desolate place". On the other hand, Luke places it in the town of Bethsaida. This is Luke 9:10-12:
Luke does not describe any journey to a "desolate place". He does, however, have the apostles say that they are in such a place.
Luke is contradicting himself - are we in the town of Bethsaida or a desolate place? The clear reason for this is that Luke used Mark's gospel as a source. Mark's account occurs in the desert all along, and thus the apostles' comment makes sense.
An infallibilist will say that the journey to the desolate place is implicit in Luke, and so I file this as Minor, but it's obvious what has actually happened - Luke has altered the setting of the story, but also copied the line from Mark, not noticing that it contradicts the change he made earlier.