win7 searches in SOME types of documents automatically

when i put a search string in, it will pull up filenames that have nothing to do with the search string, but have a 'preview' of a snippet of text within the document that has that search string.

works for:

docx
rtf
hmt/html
etc

it also seems to do it for .txt files, but doesnt show the paragraph preview - the files just appear in the search.

AFAIK this is default windows 7 behavior, you may have disabled it somehow?

im using win7 ultimate x64