Revealing mistake: When Tigress is hatching a plan to escape Gongmen Tower after they have been trapped, she looks out over the wall. But take a close look at the archers: they all move in perfect sync, indicating the same animation models were used for all of them.
Continuity mistake: When Po and the Furious Five are in the top floor in Shen's palace, the lights above them are brightly lit. After Mantis smashes the cannon through the floor, the lights turn off.
Answer: Since Po's father was presumably the only panda to attack Shen's wolves head-on, there's a chance Shen could have seen him. Plus in the flashback, Shen orders his wolves to attack Po and his mother before Po's father defends them both with his mallet.