I seem to remember a similar problem elsewhere in the bugtracker.
Unless Andrew changes things so that this 'Break-out' tool recognizes intersections of two touching Circles, I would think that the Autotrim tool is the one to use. Circles are 'tricky' little fellows. In principle you could say a Circle has infinite points and angles - these infinite points are equidistant from one point being the center! So all these points do effectively make up a continuous line or a better description would be a continuous closed curve around a center.
It is probably better to have an additional tool to 'break-out' an arc within a Circle, this way we can pick the starting and end points and break the arc in between.
what do you think?
Using your actual draft, for now if you pick a point more or less opposite the arc you wish to keep it should break out the rest.
Before...picking an opposite point.