warmanw Thank you for providing the Spine project file! It seems that the problem only occurs when the RGB key values change before and after. It also seems that the number of frames doesn't matter: if the RGB key value changes before and after, the RGB key is added in the same way, even if there are more than 10 frames in between:
The video above reproduced the problem with multiple slots selected, but in some cases the problem can actually be reproduced with a single slot selected.
When I saw this behaviour, I thought for a moment that perhaps the RGB keys were being saved deliberately, but when I deleted the recorded RGB keys, there was no change at all in the RGB value of that slot, so I am sure that they are unnecessary keys. I have created an issue ticket to fix this: EsotericSoftware/spine-editor850
Thank you for helping us to find the cause!