Your rumination on shame as a theme in the book is interesting, Sam, and, indeed, Kaukab's shame is almost excruciating to read about in the scene you describe. The amount of shame a character experiences in Maps for Lost Lovers seems to increase his or her capacity for hurting others. The character who feels the least shame of all, Shamas' missing brother Jugnu, is gentle - so gentle that he seems to attract the butterflies and moths that fascinate him.
But Nadeem Aslam gives another reason why these colorful insects are attracted to Jugnu. Working with phosphorescent materials when he was younger has caused Jugnu's hands to glow in the dark. This surreal touch, which paints Jugnu, who we meet only in flashback, as an otherworldly angelic figure, is one of many in the book. Another is the idea, most strongly held by the women in the community, that djinns, ghostly demons that cause good Muslims to stray, can be blamed for some of their troubles. (Incidentally, the Western concept of the "genie" derives from these djinns). Aslam's decadent language lends a further dreamy quality to the book.
All of this is a counterpoint to the reality of the daily lives the characters in this book live. While Kaukab dreams of fragrant roses in Pakistan, she fears encounters with English people. Our characters must ride crowded buses. They wonder if they should insert the word "fuck" when talking to English people, so that the urgency of what they are saying will come across.
I suppose I keep coming back to that same theme, assimilation, or the lack thereof. When two cultures collide, each can suddenly be observed through new eyes. To the Pakistanis, the English seem vulgar, stupid and bland, and to the English, the Pakistanis seem backward, threatening and, as Kaukab fears, smelly. Shamas and Kaukab's children, the younger generation, are able to assimilate much more smoothly, and while this frees them from some of the difficulties their parents experience, it also leads to terrible friction within the family.