Device In Many Groups In A Show

Am I right in understanding that a device can only belong in 1 Group in a Show?
I created a group with 4 custom devices. I then created another group with only 1 of the 4 devices that were in the first group so that I could control it separately. When I then made changes to the first Group, the device in both the first and second group wouldn’t respond… it seemed to only respond to changes made to the second group…… and even then it didn’t seem to be as bright as it was before when only in the first group.