Comment 3 for bug 376987

The problem seems to appear for clones of elements with any
filter, not only blured elements.

I looked into the problem a found the following:

sp_generate_internal_bitmap (pixbuf-ops.cpp) is called from
sp_asbitmap_render (cairo-renderer.cpp) for both the original
element as well as the cloned element. However, in the second
case the created bitmap is empty. So it seems that
sp_generate_internal_bitmap does not work for cloned elements.