The problem with advanced outlines is that the origin of the width duck isn't scaled together with the bline because it position depends on a calculation of its own parameters based on the blind final shape. The code to update the width points origin position isn't coded yet.
Alternatively, to scale the width of a outline (any type) once you have scaled the bline, you have two options:
1) Modify the global width of that outline layer by increasing or decreasing the Width parameter. It will affect to all width points together. Expand will do similar too but it allows to achieve negative widths. See http://wiki.synfig.org/wiki/Outline#Outline_width
2) Use Outline Grow (since 0.63.05). It is a new parameter of the Paste Canvas layer that allows to increase or decrease recursively the width of the outline layers inside the paste canvas by an exponential factor.
I hope it helps.
In the future I could try to code the update of the width points positions during bline manipulation.
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