The last 16 lines of /usr/lib/python1.5/whichdb.py are currently (note that
lines 5-7 should be between lines 13 and 15):

    # Check for BSD hash
    if magic in (0x00061561, 0x61150600):
        return "dbhash"

    # Check for BSD hash
    if magic in (0x00061561, 0x61150600):
        return "dbhash"

    # BSD hash v2 has a 12-byte NULL pad in front of the file type
    try:
        (magic,) = struct.unpack("=l", s16[-4:])
    except struct.error:
        return ""

    # Unknown
    return ""


This should read:

    # Check for BSD hash
    if magic in (0x00061561, 0x61150600):
        return "dbhash"

    # BSD hash v2 has a 12-byte NULL pad in front of the file type
    try:
        (magic,) = struct.unpack("=l", s16[-4:])
    except struct.error:
        return ""

    # Check for BSD hash
    if magic in (0x00061561, 0x61150600):
        return "dbhash"

    # Unknown
    return ""

otherwise, grabbing the magic number the second time has no effect and
yeilds an unknown db every time.