Currently, Special:MergeHistory only updates the rev_page column in the revision table. It should also update the revactor_page column in the revision_actor_temp table. Then, we can create a maintenance script that synchronizes revactor_page with rev_page for all rows in the revision_actor_temp table.

Not updating the revactor_page fields causes queries like this one to return zero in the rev_actor column for all revisions that have been moved via Special:MergeHistory.

The patch should also be cherry-picked to REL1_31, REL1_32, and REL1_33.