I contacted support about this but did not receive a very satisfactory reply, to be honest. I don't want to make one of those "mad with support reply, so go make forum topic and rant" threads, so maybe I should just log it here and hope for a better answer. Maybe even a knowledgeable player can provide a workaround:
> I had the characters "Aecarus" and "Aeca" registered on the Test Server side
> of my account before I converted to Steam. I then converted to Steam, and no
> longer have access to these characters, because they were not ported with my
> Steam account.