really stupid WP problem

I've spent the last couple of days migrating my website from ExpressionEngine to WordPress, and *almost* everything's working. I originally did a one-click install of WP into a testing subdomain, to get everything imported and set up and working before going live in my primary domain. Once all was well, I followed the WP codex instructions on moving an installation, and got everything properly moved and set up in my top-level domain.

Here's the problem -- WP in this new location seems not to think that I am the owner of its files. Permissions are set identically in both the top-level domain and in the testing subdomain (which I have not yet uninstalled, and won't until everything's okay), but WP keeps giving me messages like "if this file were writable, you could edit it." The file *is* writable, by its user. And that owner should be me. In fact, the info on the same file in the top-level domain and in the testing subdomain lists exactly the same owner (me) in exactly the same group. So why doesn't WP recognize this?

Am I going to need to remove everything from the top-level domain, do a separate one-click install, and then move my data back in? Or is there some simpler solution that I'm not seeing?