Sitemap.xml being overwritten

I have a sitemap.xml file that I have manually created in a text editor since it is actually a sitemap index file pointing to many sitemap files.

I have unchecked the “Generate Search Engine Sitemap” checkbox in Settings->General->Advanced but when I publish, RW7 still insists on overwriting my sitemap.xml file which, of course, sends Google Webmaster Tools into a tizzy.

What am I missing here besides that checkbox? Is this a Rapidweaver 7 bug or is there something else I need to do stop automatic sitemap.xml creation and uploading?