John Nolland, NT scholar out of Trinity College Bristol and Anglican chaplain, analyzes the textual criticism issues with Matthew 27:52-53. He points out that some have noticed an “interpretive difficulty” with the passage because someone “created” the story and is probably a “scribal insertion.”
None the less, Nolland concludes that even though 52-53 is absent from the Palestinian Syriac Lectionary and likely from the Diatessaron (composed all 4 gospels into one) there is a, “very slender basis” for concluding the reported event is a interpolation. However, Nolland sits on the fence on what is Matthew’s intended meaning. He probably did not make it up, but at the same time it is “impossible to say anything definite about its prehistory.” Moreover, like Moses and Elijah's appearances in Matthew 17, the appearances of the saints in Jerusalem has, “…a primarily symbolic significance.” Nolland’s own school’s statement of values remarks that Trinity is, “…committed to biblical authority. We study the Bible with integrity, seek God’s truth and pursue excellence…”
 It is located in southwest England.
Nolland John, “Preface,” The Gospel of Matthew: a Commentary on the Greek Text, New International Greek Testament Commentary (Grand Rapids, MI; Carlisle: W.B. Eerdmans; Paternoster Press, 2005), 1204.
Written by Tatian around 170 A.D. was a harmony of all 4 gospels into one. Luke Timothy Johnson and Todd C. Penner, The Writings of the New Testament: An Interpretation, Rev. ed. (Minneapolis, MN: Fortress Press, 1999), 601.
Nolland, The Gospel of Matthew, (2005) 1204
http://www.trinity-bris.ac.uk/assets/files/values_mar11.doc Accessed 10/12/2013