I noticed that too, like in the picture below.
I don’t think it would be considered a bug by core developers, i.e, it’s doubtful they would spend time tracking the root cause.
There are other glitches. For example, with a double 3D view layout, if I apply a volume rendering then display the ROI, the resizing handles appear in the slice views, but would next disappear in the green and yellow views when the mouse cursor is over them. They persist in the red view only. I did not report it since there are other ways to resize the ROI and it does not result in an unusable workspace.
So I think thet one has to accept the kind of unexpected observation you described as it is; or convince some core developer to look into it.