SVN frequently says file is locked by me in another working copy

Cleanup will not help. That's used for working copy locks, whereas you're running into an issue with files being locked in the repository itself as a means of implementing a mutex between users. See The Three Meanings of "Lock"

You probably have a client that's locking the file(s) for you in a different working copy without your knowledge (either locally or in a WC on your server), or perhaps you've got a WebDAV share that you've mounted and are opening the file(s) there which is causing a lock to be created.

On Windows, I fixed the problem by the following steps: 1. Launch Repository Browser by clicking "Repo-browser" in the menu. 2. Locate the locked file. 3. Right click your mouse on the locked file. 4. Click "break lock".