Running mIRC on "Windows XP SP2 compability mode" or "Run as administrator" didn't have effect on Vista.
$sound() seems to return nothing on .id3 and .tags, on .tag it returns 0. other $sound() properties work fine. This also is happening on Vista / 7 only.
This doesn't happen with all the errorous files, but some. Every file still containing an id3v2 tag (checked with Winamp)