Revealing mistake: When Ahsoka and Rex walk onto the bridge of the Star Destroyer, in one shot the right part of his kama is partially transparent, revealing his thigh armour beneath it. (00:08:05)
Continuity mistake: When Ahsoka tells Rex to go to the briefing, the rectangular pouch thing attached to the right side of his breastplate is missing. (00:09:24)
Revealing mistake: When R7 goes to plug in to the socket to look up information on Fives, he moves right in front of one arm of a droid charging station in the room which should be in front of him. (00:16:32)
Answer: I guess that 1) the King assumed that Ventress' droids were meant to capture the Jedi, not kill him outright. When she yells at OOM-224 to shoot Yoda, she evidently failed that expectation. 2) Sending out a bunch of Droidekas after it is plain that Master Yoda has clearly won is not a sign of good sportsmanship, either.