This is not a bug. The child bones are compensating for the scale of their parents so you have to key them. An easy way to do this is to just press "K" after you have scaled the bone, this will key all bones that have been changed.
We have a stretch goal planned so you can disable scaling inheritance. If it's just a single bone you need to do scaling on, another way to do it is to place another bone (a "null" or zero length bone) on the one you want to scale. Then move the images from the bone you want to scale to the new one and scale that instead, then it won't have any children. It results in another bone, but fewer keys.
In this screenshot I am doing exactly that to squash the torso without affecting the head and hands
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Hope it helps