There are two bugs:
Steps to reproduce:
Start with defaults.
0. Observe default label for 1-star is Poor
1. Set label for 1-star to Bad
2. Click OK
3. Observe that on Rating overlay in browser, 1=Bad, but on menu Metadata->Set Rating, 1=Poor
4. Restart app
5. Observe that on menu Metadata->Set Rating, 1=Bad (now correct after restart)
6. Set label for 1-star to Poor (this is setting it back to default)
7. Click OK
8. Check Tools->Settings:Rating Labels
9. In the dialog, 1 is still set to Bad. The value Poor is not accepted, and will not be saved.
The only way to reset rating labels to the default values is to manually edit or delete the ratingLabel line in the INI file.