Just finishing up Lord of Chaos for the 4-5 time, and I strongly disagree, it was always shown that their relationship was one of mutual respect and dedication to oaths. I can't remember exactly whether it was in 2 or 3 but there is a Moiraine internal dialog and a following dialogue with Lan about his bond chaffing. The only Ajah that routinely has intimate physical relationships with their Warders is the Green. As far as the butt scene goes, it's completely keeping with Lan's culture as a Boarder-lander, assuming Malkier share the Shinarian's shared bathhouses.