I have always manually unpacked passworded posts, so I didn't even realize Alt.Binz had this ability.
Just tested it with a passworded nzb containing the metadata (not from nzbserver) and it extracted with no trouble

@Pygmy, did you open the nzb with wordpad or something similar to verify the meta tag exists?
It's usually near the top and should look like this: <meta type="password">abcde12345</meta>