Some of the columns in the database have a maximum length (e.g. editor.name, artist.comment) but there's no maxlength set in the HTML and the server code doesn't check either. If you go over the maximum length for those fields, when it tries to insert the data into the relevant column it fails giving an error along the lines of "DBD::Pg::st execute failed: ERROR: value too long for type ..."

It also causes problems for edits which aren't immediately applied, e.g. try approving or accepting http://test.musicbrainz.org/edit/586
(originally from http://bugs.musicbrainz.org/ticket/5753 )