Update: It's apparently an issue with any extra input device being blocked from functioning as soon as the main keyboard is used.
I have three contact sheets open right now.
In the first and second contact sheets, the 1-5 keys work on the main keyboard.
In the third contact sheet, the 1-5 keys work on the separate 10-key pad that I usually use to rate photos.
However, as soon as I touched any number key on the main keyboard in the third contact sheet to rate a photo, then the 1-5 keys stopped working on the separate 10-key pad.
When I type numbers on either the main keyboard or the separate 10-key pad, they work exactly the same when inputting into any other application.
I've tested it before and after each try.
Apparently, Photo Mechanic is disabling input of 1-5 from any additional input device.
But this destroys my workflow, because I will get carpal tunnel if I try to rate photos from the same keyboard.
I use a 10-keyless main keyboard for the arrow keys, and then a separate 10-key pad to rate them with, so that my hands can rest at a healthy angle.
Sometimes I go through 15,000+ photos in a day, and when using a regular keyboard alone with the arrow keys and 10 keys next to each other, the pain of cramped and crooked hand position prevents me from even reaching 10,000. And using the top row of numbers for rating causes pain even sooner.
All those issues are only happening with the new release candidate versions such as the one expired on the 31st, and the one expiring on the 15th.