The reason that this wasn't handled properly was that up until recently, there was no way to know what tag wiki a given post was using the data available.
Since that's changed, I've gone ahead and changed the lookup to account for this case. The new behaviour is controlled by the new
EnableTagWikiTitleLookup setting, for compatibility with Data Explorer instances running off actual public data dumps, since they lack the information necessary to create the required fields.
As the database behind the public Data Explorer instance does have this data, the change should be deployed and enabled in the next revision > 2012.9.7.6.