The .shtml extension should not matter. You are rebuilding the pages before trying to view the changes, right? If so, and you still do not see the changes, don't forget to refresh the page you are viewing in your browser.
Are you using "Staggered Build?" I have had some problems with the staggered build (as opposed to "Build All") not updating the html pages, although the missing new items show up in searches. Once a Build All goes through uninterrupted, the items show up. Also, it's not a cache or refresh problem -- I checked on two different computers and three different browsers.
There's a fix in one of these threads (it was in the past week, but I don't recall where or what the name was) for Staggered Build problems. I made the changes and haven't noticed any problems, but it was rather intermittent in the first place...