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?