It was a very small thing to overlook. And nobody could blame him for forgetting it. Imagine, the ecstasy of freedom, followed by the devastation of leaving his mother behind on the burning sands of Tatooine, and THEN the shock of seeing a fight between and actual real Jedi Master and a Demon... a fight with swords of light, and invisible energy that the Jedi had spoken softly to him about... the Force.
It was a lot for a young boy to take in. And THEN he was rejected by the high council, at the same time as being informed he was special... the chosen one.
So it was no surprise that Anakin Skywalker forgot about one very very simple fact.
Watto had never removed his slave device.
What was a surprise, the greatest surprise he would ever feel - even if only for the briefest nanosecond - came when he was walking up the steps to the Jedi Temple – at the forefront of rank upon rank of silent, white armoured clones of the deadliest killer ever to have lived, as they marched to the awaiting massacre above – and stabbed Gate Master Jurrok.
Anakin was perfectly justified in not trusting the council. Especially when, as the tremors of Jurrok's death stilled echoed in the Force, Jedi Master Shaak Ti – following the orders laid down for such an eventuality – rearmed the slave device.
Palpatine sat behind his desk hours later, and watched the recording from the helmet of one of the clones in the 501st legion, presented to him from one of the few clone survivors after they'd finished their retreat from what had been a massacre. He watched as one moment, his newest apprentice gazed down at the corpse of his second Jedi kill... and the next, he was gone. Smouldering pile of dead Sith.
What had been a very bad day only managed to get worse, when Yoda, Obi Wan, and what must have been half of the Jedi Order arrived in his office several hours later.