(Don't know if this bug should be reported against Wikimedia or Mediawiki; please re-assign as you see fit.)
Mid-December 2010 the dawiki user "Pusleogpixi" requested renaming to "Pixi" in order to get a shorter name. On 29 December 2010 the process was set in motion by first moving an existing (unused) account out of the way, renaming it to "Pixi1" as per our procedure.
For some reason I didn't do my usual sanity checks before renaming "Pusleogpixi" to the new free "Pixi" account, too late realising that the "Pixi" account had already been SUL'ed from another wiki and not by the user requesting the renaming.
Upon noticing my mistake, I immediately moved the account back to "Pusleogpixi", however the edits stayed behind in the "Pixi" account, which now no longer exists, and they are still there at this time.
I asked the user to come up with another name, not already taken on any Wikimedia wiki, and then on 30 December 2010 renamed the "Pusleogpixi" account to its final name, "Pixi Uno".
Strangely, the edit counters on the Toolserver correctly attributes previous edits to "Pixi Uno", while they on dawiki's history pages incorrectly are attributed to "Pixi" and hence are missing from "Pixi Uno"'s user contributions.
The user is accumulating new edits in the renamed account, but would like the old edits back.
How do we resolve this problem?
Renaming log on dawiki:
Mis-attributed edits to the non-existant "Pixi" user:
Mediawiki says that the "Pixi" account doesn't exist:
The "Pixi Uno" account is accumulating new edits:
"Pixi Uno"'s edit counter on the Toolserver:
"Pixi"'s edit counter on the Toolserver: