Turns out this is not properly a bug, but a lack of UI feedback, which we'll definitely improve. You can't actually edit the scale in world axis, but when you focus the input box what you're seeing and editing is the local axis, therefore, in order to have a world axis for the bone head to 1.0 as in your gif, you would need to set it to 0.95 in local axis. My bad for not knowing this.
We'll still keep the issue as a reminder for the improvement we need to make. Thank you for pointing it out!
