It's not just tagging, it's star rating too. Just came here to report the bug. Here's how to reproduce it, and how to work around the problem. Note that I have auto-advance turned on
Steps to reproduce
1. Run PM
2. From the contact sheet go direct into the detail photo view
3. Apply a star rating using the number key on the keyboard
Result: Auto-advance to the next image, but the image you tried to star rate did not actually have the star rating applied.
4. Press the left arrow to get back to the image you were trying to rate
5. Apply the star rating again
Result: Auto-advance to the next image, and the image you were trying to rate actually had the rating applied.
How to work around the problem
1. Go back to contact sheet view
2. Apply a star rating
Once you've done this it appears star ratings apply correctly in the detailed image view. This seems to work until you use the crop tool, then star rating is broken again.
Neil