Strange results, while searching for my site in google

[teomax]

Hello
I just found out following thing while searching in google.

1st.Search query "my-domain.com and keyword of one page from that site"
It shows this result "my-domain.com and some page from that domain, totally unreleated to this keyword"

So i made 2.nd search "my-domain.com and main keyword of that totally unreleated page"
It shows different result again.

I repeated that proccess at least 10 times with different keywords from "my-domain.com" pages,
but google has never show me right page i was searching for.

It was really well estabilished site, but it was hit by august update.
Can anybody explained that?