Child container overrides parent container weight: bug or by design?

I have a container whose parent is root and weight is -10. I have three child containers under this container, one of which has a weight of -10, to make it appear as the first among the three child containers. The other containers' weights are -9 and -8 respectively.

However, on the node, in the categories drop-down, the child container with the weight of -10 is shown first, ahead of the parent container. Apparently, the display is based on alphabetical order and not the container weights. This isn't much of an issue, really, as the parent container has no categories. But, it seemed curious that the child containers should be shown ahead.

In the attached screenshot, 'Programmes' is the parent container.