Weird behaviour of Group & Main Camera?

Suppose we have only two groups, ‘play’ & ‘home’

Case 1:
Consider following Node Tree structure

parentNode (in group ‘play’)
|----------------Main Camera
|----------------childNode1(in group ‘play’)
|----------------childNode2(in group ‘home’)

when cullingMask of Main Camera is group ‘play’ then it displays parentNode & childNode1, which makes sense

Case 2:
Now consider following Node Tree structure

parentNode (in group ‘home’)
|----------------Main Camera
|----------------childNode1(in group ‘play’)
|----------------childNode2(in group ‘home’)

when cullingMask of Main Camera is group ‘home’ then it displays parentNode, childNode1 & childNode2.
It suppose to display only parentNode and childNode2 like previous case1?