You're right, that change fixed it for somebody else but it breaks it for me.
This is the script as I'm using it right now and it's working for me:
$if($in(%artists%,;),
$set(DISPLAY ARTIST,%artist%)
$if($in(%artist%,feat.),
$set(artist,$rreplace(%artist%,\\sfeat.*,))
$setmulti(GUEST ARTIST,$replace(%artists%,%artist%; ,))
,
$copy(artist,artists)
)
,)
$if($in(%title%,mix by ),
$if($not(%remixer%),
$set(remixer,$rreplace(%title%,.*mix by ,))
$set(remixer,$replace(%remixer%,\),))
,)
,)