The current implementation of custom processors is broken when it merges the data together:
foreach ( $this->processors as $processor ) {
$data = array_merge_recursive( $data, $processor->getExtractedInfo() );
}The recursive merge will mess up merging of things like $wgGroupPermissions and anything else where there are common keys. Let's just remove it from 1.25 for now since there are currently no users of it, and re-evaluate how to implement it in 1.26, or whether we even need it.