Strange 'Index' site search results

I have not noticed this before.

[Rik762]

Whilst checking site:www.example.com "example+com" today I noticed that there were fifty or so entries such as Index of/subdomain/brand with some giving the URL as www.example.com/subdomain/brand/?D=A instead of www.example.com/subdomain/brand/brand.html

This just links to a text version of what I imagine is on the server, not to the page itself. Should this be there - have I done something wrong and is it considered duplicate content in any way?

With thanks to you more enlightened beings.

[edited by: tedster at 12:14 pm (utc) on April 19, 2006]
[edit reason] change specifics [/edit]