Hi,
I believe there is a problem with the way bounding boxes are calculated. At the moment the calculation assumes that lines have a
Round< join and cap style if the stroke is visible. This means, for
example, that the bounding box of a 30-60-90 degree triangle does not preserve the proportions of the triangle and that a triangle with a Miter join style extends past the bounding box. It also means that a non-horizontal or vertical line with a Square cap extends outside the bounding box and that a line with a Butt cap doesn't reach the bounding box. I can't see any advantage to this particular definition.
A better choice for defining the bounding box would be to use the entire visible area covered by an object.
Advantage: More intuitive and probably what most people would expect.
Disadvantage: More CPU intensive? May not be what is wanted for lines with markers - could ignore.
There may be occasions where a different definition could be advantageous such as defining a bounding box assuming a Miter join style or using only the nodes (both preserve the proportions of regular objects). Perhaps these could be added as per object options.
Tav