I think I remember seeing that issue discussed on the userscripts page. If there are old versions available you might find one from before he “fixed” that.

Edit: Oh, or maybe use wildcards in your search words. If your search word is “*test*” it’ll match any word containing test as a substring (just tested that and it works) although it’ll replace the entire word with your replace word, so it may take some more work to get a RegExp working to match any word with it as a substring, and then only replace the specific part you want it to