r19631 changed the logtitle from $wgTitle to the old username. User renaming before this revision are list under 'Special:Renameuser' (see url).
Please create a script to migrate these log entries to the username. Thanks.
Please give a hint, when there is need for a new request to do this on all WMF wikis. Thanks.
In the log dump from de.wp I have found 8 entries with a empty action and type, but logtitle=Spezial:Renameuser ('Spezial' is localize 'Special'). Maybe it can change by the way. (ids: 147479, 148176, 148177, 148889, 153335, 153336, 154632, 160549)