This bug happens to rigify rig as well (and of course it happens it uses copy transform constrains) if you scale the shoulder bone for example.

Hey, wait a second. i can reproduce the same bug without turning off inherit rotation. If I use default bones with the following settings:

You can download the .blend file from here.

Hi,
sorry I am away from my computer for a week or so. Once I return I will upload any files you need.