gdk_pixbuf_composite leaves artifacts in new image

[Todor Todorov <ttodorov gmx net>]

Hello list,

I am trying to create a thumbnail from a digital image, which should not 
exceed 128 px width or height. After loading the image, I apply the EXIF 
orientation information, if available. In order to prettify the 
resulting display, I would like to place the pixbuf horizontally 
centered onto another transparent pixbuf with dimensions 128x128 px. 
Here is (part of) the code I use (removed the error checking for 
simplification):

gchar *imgSrcName;
GdkPixbuf *src, *interm, *result;
guint width, height, xOffset;
int i = 0;
...
src = gdk_pixbuf_load_from_file_at_scale( imgSrcName, 128, 128, TRUE, 
NULL );
result = gdk_pixbuf_new( GDK_COLORSPACE_RGB, TRUE, 
gdk_pixbuf_get_bits_per_sample( src ), 128, 128 );

interm = gdk_pixbuf_apply_embedded_orientation( src );
gdk_pixbuf_unref( src );
width = gdk_pixbuf_get_width( interm );
height = gdk_pixbuf_get_height( interm );
while ( i < 2 )
{
        gchar *save;

        gdk_pixbuf_fill( result, 0xffffff00 );
        xOffset = i++ * ( 128 - width ) / 2;
        gdk_pixbuf_composite( interm, result, xOffset, 0, width, 
height, 0, 0, 1.0, 1.0, GDK_INTERP_NEAREST, 255 );

        save = g_strdup_printf( "test%d.jpg", i );
        gdk_pixbuf_save( result, save, "jpeg", NULL, "quality", "100", 
NULL );
        g_free( save );
}
gdk_pixbuf_unref( interm );
gdk_pixbuf_unref( result );

The resulting images can be seen at:
[1] http://www.inselpix.com/img/833790624900.jpg
[2] http://www.inselpix.com/img/478403985121.jpg

As you can see, the result is OK only if the xOffset on translation is 
0. The centered version shows artifacts on the right border of the 
image. And it does not make a speck of difference, if the interpolation 
type is _BILINEAR or _HYPER ...

Could anyone please help in solving this ?

Regards

Todor