Right now, if a Wikibase change is the last change for a given Wikipedia (client) page, then it will show that page multiple times in the watchlist. We are currently treating a Wikibase change like a log entry, which do get shown multiple times in the watchlist. Wikibase changes should be shown just once.

The query as performed to generate the watchlist:

SELECT rc_id,rc_timestamp,rc_cur_time,rc_user,rc_user_text,rc_namespace,rc_title,rc_comment,rc_minor,rc_bot,rc_new,rc_cur_id,rc_this_oldid,rc_last_oldid,rc_type,rc_patrolled,rc_ip,rc_old_len,rc_new_len,rc_deleted,rc_logid,rc_log_type,rc_log_action,rc_params,wl_notificationtimestamp,page_latest,ts_tags FROM `recentchanges` INNER JOIN `watchlist` ON (wl_user = '2' AND (wl_namespace=rc_namespace) AND (wl_title=rc_title)) LEFT JOIN `page` ON ((rc_cur_id=page_id)) LEFT JOIN `tag_summary` ON ((ts_rc_id=rc_id)) WHERE (rc_timestamp > '20121229191341') AND (rc_this_oldid=page_latest OR rc_type=3) ORDER BY rc_timestamp DESC

To fully support wikibase changes in the watchlist, we need to insert a null revision and have a unique revision id to insert into the rc_cur_id field of the recentchanges table.

It may be possible to use a hacky GROUP_BY clause in the watchlist query, a subquery, or other uglyness to make it work without the null revision, but that would make the watchlist query a bit slower.