Why did Malaysia lie so brazenly about the 'verbal understanding' with President Diosdado Macapagal about elevating the Sabah case to the International Court of Justice?

Senator Jovito Salonga (standing) seen talking to the President and Founder of the University of Cagayan Valley who also happens to be the grandfather of one of the Admins and creators of the Defenders of the Philippine Sabah & Spratly Claims Community.

Senator Jovito Salonga, in the introduction of his 30 March 1963 point-by-point reply to Senator Sumulong's attack on the validity of the Philippine Sabah claim, wrote a year later:

"It was agreed that the Sabah claim would be settled by peaceful means, but the "verbal understanding" between the Tungku and Macapagal regarding the elevation of the case to the International Court of Justice, was denied later by Malaysia." 

Why did Malaysia lie so brazenly about the 'verbal understanding' with President Diosdado Macapagal about elevating the Sabah case to the International Court of Justice?

TO READ Senator Salonga's "A Point-by-Point Reply to Senator Sumulong's Speech on the Philippines' North Borneo (Sabah) Claim", click on this link here: Jovito R Salonga Journal