dropshadow operation: grow_shape is ignored if negative but description says negative values contract the shadow.
I'm not sure if the right fix is to disallow negative values and update the description, or to implement shrinking; a median blur is used for the growing.
In dropshadow.c i see,
if (o->grow_radius > 0.0001)
{
gegl_node_link_many (state->input, state->grow, state->darken, NULL);
}
else
{
gegl_node_link_many (state->input, state->darken, NULL);
}