-INSERT INTO backlog (time, bufferid, type, flags, senderid, message)
-VALUES (:time, :bufferid, :type, :flags, (SELECT senderid FROM sender WHERE sender = :sender), :message)
+INSERT INTO backlog (time, bufferid, type, flags, senderid, senderprefixes, message)
+VALUES (:time, :bufferid, :type, :flags,
+ (SELECT senderid FROM sender WHERE sender = :sender AND coalesce(realname, '') = coalesce(:realname, '') AND coalesce(avatarurl, '') = coalesce(:avatarurl, '')),
+ :senderprefixes, :message
+)