g1smd - 11:36 pm on Jun 28, 2011 (gmt 0)
This is at least the second report of similar such things happening in recent days. There's a much longer thread around these parts with a conversation already in progress on this topic.
It might be internal linking problems within your site, combined with lax URL rewriting rules in your .htaccess file. It's worth running Xenu LinkSleuth over your site.