blur clipping with straight lines

using the bezier curve/straight line tool
draw a diagonal line so the end points are near the corner of the bounding box
in fill and stroke in stroke style increase width to 8px or so
change cap to rounded and then increase blur
instead of getting the expected rounded blurred edge you get it clipped by the bounding box
if you increase it far enough (for me beyond usable) the bounding box expands and starts
including the blur again

version is extra/inkscape 0.91-22 in arch linux

attached is an example