Audio problem: When Frost first enters the conference room with the rest of the members of the house, the older member with the symbol tattooed on his forehead scolds Frost about how he's not a pureblood. In a shot down the table (probably only noticeable in widescreen), you can see the guy on the right side of the screen, but his mouth isn't moving, even though you hear him talking.
Audio problem: Right before Blade throws his sword to retrieve his EDTA in the final battle, he leaps to his feet as Frost attempts to stomp downwards on him. As Frost's foot his the concrete ground (or Blade's shoe, as it's unclear from the shot as the impact is out-of-frame), the audio features an incredibly loud and out-of-place flesh-on-flesh punching sound effect, instead of a proper "shoe stomping concrete floor/Blade's boot" sound that should have been played.
Audio problem: Just after Quinn has been nailed to the wall at the beginning of the movie, he makes some strange noises and then starts talking in "vampire language." This has obviously been dubbed in post-production.
Answer: I don't think it's so much a memory as it is Blade just equating Karen with his mother in that moment. The only way to convey his thought process to the audience, though, is to show his mother onscreen.
Phaneron