[raster] ST_AsRaster(geometry, rast) do not align raster properly

[pracine]

I made the queries to be easily displayable in OpenJump...

I have a geometry:

SELECT ST_Asbinary(ST_Buffer(ST_SetSRID(ST_MakePoint(2, 1), 0), 1.3));

and a raster:

SELECT ST_Asbinary((gv).geom) geom, (gv).val
FROM (SELECT ST_PixelAsPolygons(ST_MakeEmptyRaster(4, 4, 0, 0, 1, 1, 0, 0, 0)) gv) foo

and I want to rasterize that geometry aligned on this raster:

SELECT ST_Asbinary((gv).geom) geom, (gv).val
FROM (SELECT ST_PixelAsPolygons(
               ST_AsRaster(
                           ST_Buffer(ST_SetSRID(ST_MakePoint(2, 1), 0), 1.3),
                           ST_MakeEmptyRaster(4, 4, 0, 0, 1, 1, 0, 0, 0)
                          )
             ) gv 
     ) foo

The produced raster is not aligned properly and the extent do not encompass the geometry.