BuddyPress.org

* You’ve deleted all the content (visible and invisible) from your root folder

– Have not done this, but I did create a new subdirectory and installed WPMu in that location.

* Your using a blank DB that has a different name, username, and password from any that you’ve used before

– Check.

* You’ve cleared your browser’s cache

– I’ve done this with previous testing, but not with this new install. I’ll try that.

* You’ve downloaded a new copy of WPMU and installed it, creating brand new wp-config and .htaccess files

– Check.

* You’ve downloaded the newest BuddyPress trunk (if running bleeding edge). If using a tagged version of BP, then you’ve downloaded that version again to have a fresh, clean copy. You then manually install BP and then activate it.

– Check (revision 1903, as noted).

* You have no other themes installed in wp-contents (other than the default WPMU and BP themes)

– Check.

* You have no other plugins except BP (and possibly the default plugins that come with WPMU)

– Check.

—-

So, it seems that clearing my browser cache and clearing the root folder might be the only issues. I’m imagining that the latter assumes I’ve installed in root, which I haven’t; I have a single-user WP blog there that’s not going anywhere. I could install to my local machine (which I’m likely to do anyway), but that wouldn’t seem to invalidate this particular phenomenon.

As to browser cache, I’ve cleared that before without affecting results, and will do so now; but that would seem to suggest it’s not critical. I’ll leave a note after I’ve tested it, though (don’t want to while replying, for obvious reasons).