Search Sensitive Weirdness

Varying search results

[activeco]

After looking at my logs, I noticed a search term from Y which I couldn't reproduce in search results; my page was nowhere to find.
After applying Case Sensitive phrase exactly as in the log, my page suddenly appeared on the very first page of search results.

I wouldn't call it regular Yahoo feature.
I played with some popular phrases and could find just a slight differences in rankings.
However, in many cases, although seemingly similar, the results tend to exclude/include one or two pages/sites completely from several result pages down.

E.g. when searching for d.. c...... , very famous electronics producer occupies 2nd & 3rd place.
A search for d.. C.... completely wipes the producer out. I couldn't find them in the first five result pages. (Similar thing happened to my pages.)

For even bigger mistery, the producer's returned page does not have a single occurence of low case phrase, where it ranks well.