SVN submission — WP repo not picking up updates correctly?

I’ve authored a plugin and I’ve submitted it to the WordPress repository so it’s available for download. No problem.

But now I’ve run into problems when I’ve attempted to publish updates to the plugin. I submit the changes, the WordPress page for my plugin shows the changes to the readme.txt file, but the version that’s available for download HAS NOT CHANGED. It’s really frustrating, and I can’t find any documentation that clarifies this.

Here’s what I’ve done:

1. Updated the “Stable tag” parameter thereadme.txt file.
2. Updated the Changelog and Upgrade Notice sections in the readme.txt file.
3. Updated the information header in my plugin’s main file to reflect the new Version attribute.
4. Submitted my changes to the SVN trunk.
5. Made an SVN copy to copy the trunk to a named branch using a command similar to the following:
   svn copy https://wp-repo.com/my-plugin/trunk https://wp-repo.com/my-plugin/tags/1.2.3

I’ve submitted many SVN changes and tagged new versions, but no matter what I do here, the plugin page that WordPress displays is always the first version of the plugin — my updates are ignored, so the plugin users never get notified that there is a new version available. The only way to get the latest version of the plugin right now is by using SVN.

The only quirk I can think of is that my information header is in a file named index.php instead of a file that shares the name of my plugin. I haven’t seen any documentation that says it’s required to use a specific file name for the file that contains the plugin info header, but I’ve seen enough crufty bugs in the WP dev cycle to believe that such a low-brow minutiae could cause problems.

What am I missing?