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Google searches are NOT case sensitive. All letters, regardless of how you type them, will be understood as lower case.
By any chance is one of those search terms "OR", which is taken as a Boolean operator when it's typed in uppercase?
Compaining about Some Google Missteps (seomoz) [seomoz.org]
Scroll down to about one third of all comments.
It's basically a QnA by Matt Cutts.
On why caps DOESN'T make a difference.
Part of the issue is that "it" can be a stopword in some cases, and upper/lowercase makes a difference, e.g. IT usually means something different than it.
There are very very few words where capitalizing makes a big difference in the word sense. (...)
That said, I have heard people ask about this before. I'll send a pointer to your post to some webranking people, but I'll mention that in the past we've viewed as not as big a help as other things we could do.
Perhaps this has something to do with your problem.
Or perhaps not.
I WOULD SAY ABOUT 90% OF EVERYONE ON THE NET HATES ALL CAPS THESE DAYS AND I DON'T THINK IT MATTERS IF YOU'RE #1, THEY STILL WON"T CLICK ON IT...