In the final showdown between Ivanhoe and Brian de Bois-Guilbert, Ivanhoe cuts Brian de Bois-Guilbert's shield in half. In the next scene we see Brian de Bois-Guilbert turn his horse for a new charge, and his shield is undamaged. But when he reaches Ivanhoe, the shield is broken again.
Ivanhoe's shield is punctured by Bois-Guilbert's lance in the joust. In subsequent scenes the hole disappears, then reappears.
In the second joust at Ashby, they joust with blunted lances. During the charge, the templar's lance clearly lacks the metal end-cap. In the next shot, when he makes contact, the cap is in place.