Audio problem: During the wild boar hunt, they are interrupted by Aleander who says, "Prince Frederick of Saxony. He refuses to surrender Luther to you, Your Holiness," but nothing matches his lip movements. He utters a couple of syllables, at most, out of sync with the two full sentences heard in the movie. (English DVD version).
Other mistake: When Leo X is hunting a wild pig, a poem is recited which mentions a boar (at least in the german version). But while the pig is running you can see it is a sow (from its longish nose). After the pig is hit, you can even see the teats. In the next shot the sow is supposed to look like a boar: It now has the characteristic big teeth of a boar.