Continuity mistake: Rumpelstiltskin looks completely different in this movie than he did in the previous film Shrek The Third; Prince Charming momentarily talks to Rumpelstiltskin in the tavern during the third film, and the character looks completely different, has a different voice and different demeanor.
Donkey: Man, you are a cat-tastrophe.
Puss in Boots: And you, are ri-donk-ulous.
Question: Why did the king and queen disappear when the king signed the contract? The deal was that Fiona will be saved from the curse if he did - but Fiona wasn't saved at all. Was the contract void from something?
Answer: Rumpelstiltskin used a contract that 'made all their problems disappear'. He didn't reference any specific problem and the king and queen assumed it would cure the curse. However, it just makes the king and queen disappear, and since they have disappeared, they will no longer have any problems.