- $prevTags = $dbr->selectField( 'tag_summary', 'ts_tags', $tsConds, __METHOD__ );
+ // $prevTags can be out of date on slaves, especially when addTags is called consecutively,
+ // causing loss of tags added recently in tag_summary table.
+ $prevTags = $dbw->selectField( 'tag_summary', 'ts_tags', $tsConds, __METHOD__ );