Interestingly, I renamed index.fwx to about.fwx, hit it in the browser, and got a good about.prg and about.fxp files and they returned good html in the browser.
I renamed two of those files back to index.fwx and index.fxp, and they returned good HTML to the browser.
I then edited index.fwx. index.fxp was not regenerated, and index.prg was not created. I still got the HTML from the previous version, compiled as about.fwx.