That's not a bug.

Zotero has always renamed files saved from the web automatically, and if you've been running Rename File from Parent Metadata manually, you've been wasting your time. If you just save normally and look at the Filename field in the right-hand pane of the attachment, or right-click → Show File, you'll see that the file is named correctly without your doing anything.

What we changed in beta 23 is having a manual Rename File from Parent Metadata not change the attachment title needlessly if it doesn't already match the filename. The attachment title is meant to be different, and if anything it was a bug that it was changed unnecessarily before. Read this thread for more details.

The only issue after this change is that in the cases where Rename File from Parent Metadata is actually changing something, it's not immediately clear that that happened. We plan to add some sort of indicator for that. But again, if you're just saving normally, there's no reason to be running that manually unless you changed the parent metadata (and we plan to do automatic renaming on changes in a future version).

The linked thread gives examples of cases where differing attachment titles are important ("Submitted Version", "Snapshot", etc.), and explains that all the metadata in the filename is already in the parent row, so showing it again would just be distracting clutter.