Can't set "Treat similar words with diacritics as different..." option

I want to change the search option in Outlook (and/or Windows 7) to "Treat similar words with diacritics as different words". I've followed the instructions (Change advanced indexing options) precisely: In indexing options, click Advanced, then check "Treat similar words...". This brings up a dialog box saying the index will be rebuilt upon clicking OK. I did so, but rather than taking "several hours", only a few seconds went by before the hourglass disappeared. I then clicked OK to Advanced Options, then Close to Indexing Options. However when I check again the "Treat similar words..." option is once more unchecked!

How can I get this to work?

Thanks! Following the instructions in your link brought me to exactly the same options window that I'd already reached before via both Outlook and Control Panel, so when I went through the motions again I was sure I'd get the same non-result as before. But lo & behold - this time it worked! Windows never ceases to amaze me!