position in Yahoo,AOL and other Google power by

Different positions

[xMadx]

Hello,

I have 2 web sites, which rank #2 and #4 with key1 key2
My 1st site which rank #2 in google, rank #1 in AOL & ALEXA, but doesn't appear in Yahoo or in HotBot(using google option)
My second site have the same position in google, in AOL, Alexa, Yahoo, HotBot.

I use this syntax for my search:
[google.com...]

Why my 1st site doesn't appear in Yahoo?
How explain this difference?
What filter is used in Yahoo?
Both of my site are in english, located in the same server (different ip)

Thanks

[amazed]

yahoo filters double urls in results.