It seems this bug occurs when the filters effect expands outside of the shape bounding box area.
As a work around I group the shapes with a large invisible quadrangle around them before applying the filter.

ivan
loonquawl wrote:Are you sure there is a line? With me (0.46 on XP), the Filter often does seem to generate a line, but really only has troubles rendering the filter. Or, if there positively is a line -> In the Filters Dialog, there is a Filter General Settings Tab, in which you can set the area that the filter will work on - perhaps it is too tight in your case