Obama not Forthcoming on 1981 Private Trip to Pakistan

Having read about it extensively, I thought I knew all about Barack Obama's background, many elements of which are troubling (Rev. Wright, etc...). From Indonesia to his Muslim family in Kenya most of his background has been explored. However recently I came across a few pieces of the puzzle that have been mostly unknown to the public:

While at Occidental college he became close friends with two Pakistanis, Mohammed Hasan Chandoo and Wahid Hamid. In 1981 he traveled with Mohammad Hasan Chandoo to Pakistan and stayed there for about three weeks. It is rather unusual for a less-than-wealthy college kid to choose far-away Pakistan as a summer break destination, but not necessarily suspicious. For some reason however, Obama has never publicly cited these relationships or his time in Pakistan. Why not?

In his book "Dreams from My Father," Obama does talk of having a different Pakistani roommate when he later moved to New York, a man he calls Sadik who "had overstayed his tourist visa and now made a living in New York’s high-turnover, illegal immigrant work force, waiting on tables." Strangely, Mr. Obama, the campaign and his publisher have not provided any details about the identity of Sadik.

All of this new info probably just represents Innocent gaps in an otherwise extensively researched background. However, why all the secrecy about his travel to Pakistan in 1981? Why no mention of it before in public or in his two books about himself? Why the mystery about "Sadik"?