The other day, by way of example, I was giving Google a hard time. Then after seeing if they made any changes to the SERPs based on that post, which they did, I noticed MSN's bad behavior.
Yesterday, I noticed that MSN indexed a link to an Ask Jeeves SERPs page. For example, see a search at MSN on big blue pineapple chair and then scroll down to the 3rd result. You should see.
Ok, so they didn't write a piece of code to block results from Ask's SERPs page. But then I look again today, to take some screen captures and noticed that MSN's own SERPs are included in MSN's index.
I started a thread on the topic at Search Engine Watch Forums where a member adds that MSN has not only indexed that SERP but about 60,000 other Ask Jeeves search results pages. So then I decided to check the other search engines. Over 70,000,000 of its own engine, but it seems to be staying off Google & Yahoo for the most part.