Batch Rename does not preserve file extension
EDIT
The issue was resolved by resetting standard workspaces. I reset those, the preferences, and dumped the cache all at the same time. I'd previously tried only the latter two, but not the workspace reset.
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I have reported this issue here before but I was asked to post here at the Adobe community forum, so I'm posting again.
In the past, I could select files, go to Batch Rename, input my renaming criteria, and the changes would be made without affecting the file extension. However, for quite a while now, I have had to manually add a "new file extension" line to my Batch recipe in order for the files not to drop a file extension completely. See attached images to see what happens when I leave off the appropriate extension in the recipe.
Nothing I've tried has worked and I've searched various Adobe forums off and on for ages. I just updated to the new 10.1.0.163 Bridge today (that released alongside Photoshop 21.2.0) AND reset my preferences.
Nothing helps. Any ideas?

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Kukurykus commented