Other mistake: When the main characters are in the motel and they hear the moth flying outside the window, Stu, the creepy deputy with the glasses, picks up a shot gun and racks a round into the chamber. In the next shot of all of people firing at the moth through the window, Stu is now holding his revolver and fires with it. When he runs of out ammo with the revolver he picks up the shotgun again and before firing racks the pump again. Since he already did that the gun should have ejected the unfired shell that was already in the chamber from earlier, but no shell is ejected.
Other mistake: Right before Blade confronts Frost at the end, he is shown beating up several henchmen vampires using punches and kicks, before grabbing his sword. As he grabs his sword, you see several of the henchmen vampires "burning up" in the background. However, it was earlier established that to "burn up", vampires had to be killed by traditional means. (Staked with silver, exposed to sunlight, etc.) So it makes no sense for these henchmen to burn up from only being punched/kicked. It can't be due to his sword, as he twirls it in front of them, and only after they are already burning up.