Hey,
New one on me - the ban has never been quashed and was indeed applied in 2006. There was a revision of the offence system at about the time that access was gained in 2009, for now my assumption is that something in that revision process allowed the access, probably as the ban and mute status for all accounts was recalculated in the migration process.
I can see there was a period 28 January 2009 through 15 February 2009 where it appears the account could be played despite having a perm ban.
We will, of course, look into this - but I wanted to give you a response right now - albeit a little vague.
On a side note, if you submit a ban appeal now there is a really good chance it will be granted, it's a very old ban and is not for a high risk offence.