graeme_p - 8:47 am on Jun 12, 2013 (gmt 0)
No idea why, but if it worries you (and it does not feel right to me either) why not configure your server to either:
1) 301 redirect requests to those domains to yours
2) return a 404 if the domain is not yours.
You must either have your own server, or your own IP for this to work, so you probably can configure the server (at least with .htaccess which is all you need).