Particular

Synfig puts an interesting twist on how positioning and layering
work, as opposed to usual graphics programs. Each object that
one creates is assigned a distinct layer, in top position. Only then
can one group them(or not), and apply effects.

Below, the first image has the blur effect within the group, the second

on top.

But there are other considerations, and that is the blend mode.

Composite is the ususal, but straight will actually make things on the

bottom disappear.

My wholly blurred image above has a straight blend mode, and the outlines

of the red circles are gone. (I've raised the circle regions with the raise level
command on right-click the level).

The most surprising thing, though, is that the smooth-move tool will run a circle

around no problem, but a rectangle will not budge. Touching the green corners

merely resizes. One has to choose it, and press   Crtl + A, and one can then move

it in a piece from the bright green 'handles'.   

Resize:  

Move: