Did Lee Hsien Loong studiously avoid Najib Razak in US-ASEAN Summit?

Prime Minister Lee Hsien Loong was on a working visit to the United States of America (USA) from 10 to 16 February 2016. He met many business and political leaders during his trip, including:
CEO of Apple, Tim Cook and head honcho of Facebook, Mark Zuckerberg

And of course the host of the US-Asean Summit, President of the USA, Barack Obama.

He even took a wefie with Cambodian PM Hun Sen, Vietnamese PM Nguyễn Tấn Dũng.

But guess who he seemed to studiously avoid being photographed with?
Malaysian Prime Minister Datuk Najib Razak.
Najib was of course mentioned in the group picture of the Special US-ASEAN Summit.

It would have been not only awkward, but also undiplomatic for the PM to not mention him when he is in the group picture.
But the pally warmness between the two evident from the past meetings seems absent now.

In January last year PM Lee reiterated Singapore’s zero tolerance for corruption:
“Fortunately, in such a complicated world, Singapore is the shining exception. But never take this for granted. Not only must we uphold our high standards, which already takes unremitting effort, but we must enhance them, and maintain our zero tolerance for corruption, regardless of the rank and seniority of the officers who may be involved. As the Chinese say, you must go after the “Tigers” and also the “flies”. Never let corruption take hold here, because once it takes root, it will be very difficult to weed out.”
Perhaps he wanted to be avoid being seen in the company of a Prime Minister who is embroiled in allegations of corruption?