There is a bigbug but no time to file it quite properly :

« '''''Update artist credits to use the new artists name''''' » checkbox status is invisible for voters !

There is a suggestion for checkbox text change to something more clear like :

« ''Update '''merged''' artist credits to use the '''target''' artists name'' »
But no time to file it ATM..

cf.
http://musicbrainz.org/edit/14460760
http://chatlogs.musicbrainz.org/musicbrainz/2011/2011-05/2011-05-20.html#T14-09-07-461681
http://musicbrainz.org/edit/14476843