Three Domains Pointing same I.P with same Content

Is it a problem with Yahoo

[webnewton]

It's a client's site where 3 domains are pointing the same I.P with identical content. (say www.compnayname.com, www.companyshortname.com and www.companyproduct.com)

www.compnayname.com is the oldest among the three and is running since last 4 years while the other are some 8 months old. www.compnayname.com is also listed with yahoo directory.

Till April 04 an old site was being run through www.compnayname.com and new sites were running on the other two domains. This new site was also being run through a folder from the www.compnayname.com domain. This old domain was in top of the SERPS for a lots of keywords on Yahoo. However in April as i replaced the old site with the new one on www.compnayname.com. Within the next 10 days the site was gone from the SERPS.
Initially i didn't bother as i thought that this has happened due to replacement of the site with the new site and that the rankings will jump back and because the ranking as Google were stable. Last week i was shocked to see that the site is not even in the index with Yahoo though it's still listed in the directory.
What could have gone wrong. I personally feel that Yahoo has penalized the domain as the same 3 domains ar pointing the same I.P with identical content. I have been made to draw this conclusion after an another client lost his site on Yahoo. He'd pointed a domain with duplicate content against the site handled by me without my knowledge.

Has anyone else experienced the same? If yes what is the best way out. Will sending an request with Yahoo help?
I saw a quite simmilar post here [webmasterworld.com...]

[webnewton]

is anyone aware of any such penalty by yahoo.

[Marval]

Hope this gives a little help - it depends on how you are doing the duplicate content - if you are 301 to the other domains - it might hurt if you also have separate links to all three domains - if you alias the domains on the server side to look like all the same site, then it shouldnt matter and Ive actually seen some sites do it recently to get around the old site inclusion penalties that happened from the Inktomi problems. In those cases the people were listed in the directory for the main site and had a "few" alias domains pointing at that content and were eventually included in the web results. I know of a few websites that have done that and are listed in the directory and still havent been able to shake the Inktomi penalty so its more of a toss-up?

[webnewton]

Any one else encountered the same problem.