why The President fumbled-Grammar?

This has reference to "Flubbing his lines" by Steven Pinker in the Times of India dated 23rd Jan 2009.
I know nothing of the U.S constitution. However since Mr. Pinker writes"(Roberts)unilaterally amended the constitution by moving the adverb “faithfully” away from the verb." I surmise that the constitution probably uses the form "will faithfully execute...".
Now Mr. Obama is a trained lawyer and it is extremely unlikely that he would not know the wording of the oath. And besides it is quite likely that he has probably done a dress rehearsal with the oath in the "will faithfully execute...". format. He was probably surprised at the unexpected wording change and this has little to do with "Freudian slips" or the "unconscious" on the President's part. Mr Pinker is bang on Target.
Some in the media Rajdeep Sardesai included announced gleefully that it is not just the Reporters but also presidents who fumble.But In this case it probably was not the president's fault.
It is worthwhile noting that according to syntactic theory Adverbs or Adverb phrases are 'adjuncts' and there fore moved to other positions in the sentence. What this means is that from a syntactic view point "faithfully" is not essential and therefore can occur before or after the verb phrase .It is indifferent between "will execute....faithfully" and " will faithfully execute...". The only exception that I can think of is the adverb "not". The wording is more a matter of style and Mr. Roberts is entitled to his style but probably not on the matter of an agreed oath of office.
The question of correct grammar is also tied to whether Normative Grammar or Empirical Grammar is meant. This in turn needs a view on the existence of a "Universal Grammar" propounded by Noam Chomsky.
I personally believe people don't go around with either a Normative grammar book or a hard wired "Universal Grammar" in the head. People I think can make sense of both of the constructs above and similar ones without the faintest notion of an adverb. And I think they will invariably associate "faithfully" with "execute" irrespective of position. Language is more a matter of convention and these keep changing. Yesterday's noun can become today's verb e.g google to googling. Besides people can make sense of ungrammatical constructs in context.