An excerpt from Beginning Java Objects: From Concepts to Code by Jacquie Barker:
Your client comes to inspect the work, and he is terribly disappointed. One of the reasons he had selected blue stars as a construction material was that they are extremely energy efficient but, because you used nails and mortar to assemble the stars, they have lost a great deal of their inherent ability to insulate the home.
To compensate, your client asks you to replace all of the windows in the home with triple-pane thermal glass windows so that they will allow less heat to escape. You’re panicking at this point—swapping out the windows will require you to literally rip the walls apart, destroying the house.
When you tell your customer this, he goes ballistic! Another reason he selected blue stars as a construction material was because of their modularity, and hence ease of accommodating design changes but, because of the ineffective way you assembled these stars, they’ve lost this flexibility as well.
I absolutely have no problem understanding the first he had selected. But, why do you think in the second instance, the had has gone missing? Although I think I have, sort of, a general feeling why that might the be case, I still would like to receive a more grammatically rigorous explanation as to why this kind of thing happens when we first use the past perfect and then shift it to a simple past tense when there is a need to use the same idea again.