Google Always Indexing Page "/a"

I have been searching for an answer to this with no joy so far so I will give it a try here and see what happens.

On several web sites I have developed, I recommend that the owner submits their site to Google Webmaster Tools. No problem there.

However, in most cases, their reports show Google has indexed a file called “http://www.domainname.com/a” where domainname is the owners domain name.

In all 4 cases, the Webmaster Tools reports 10 pages linking to the URL. But when I visit all 10 of the URL’s and do a search, none of them contain a link to the “http://www.domainname.com/a” .

Any thoughts on this? I am completely stumped here.

Permalinks for ALL sites are set to Custom with a value of “/%category%/%postname%/”.

Thanks,
Erbuc