I wish I knew the answer to your question. I am also perplexed about many of the "Genetic Ethnicity" breakdowns that I have seen from AncestryDNA, including my own. Since they are not releasing the raw data, there is no way to further investigate or get a second opinion in regard to what they are reporting. At 23andMe or FTDNA, I always advise people wanting to clarify their admixture results to download their raw data to utilize third party applications - some of which are very good. Right now all I can say is that you can test at one of the other companies for a second opinion and access to your genetic info (which does belong to you after all). 23andMe just announced at Jamboree that they are updating their Ancestry Painting to include about 20 populations. I wrote about it here: http://www.yourgeneticgenealogist.com/2012/06/23andme-announ...
Please keep us updated if you get any answers from AncestryDNA.