What is the point of a light group with one light?
That’s not the point. Even with more than one light this behavior occurs.
And the reason why I want to use lightgroups is to have an abstraction layer between my lights and my automations. By using a lightgroup, I can address all my automations to the lightgroup. If a bulb needs to be replaced, or a bulb needs to be added, I can just change the members of the lightgroup and everything still works.
Yeah, just my fault: I used “button” on lightgroup and “light” on single light. That’s the difference. If I use “light” on a lightgroup, it appears just the same as a single light.
So “problem” solved.