Mapnik PGRaster Plugin creating 8x8 tiles with visible boundaries

I have used the latest addition to Mapnik PGRaster plugin (https://github.com/mapnik/mapnik/tree/2.3.x) by Strk(https://github.com/strk/mapnik/tree/2.3.x-pgraster) and merged recently

I am able to get the images properly projected on the Map. But the images are tiled into 8x8 manner and I could see the boundaries of the images at certain zoom levels.

The boundaries are between the 8x8 tiles I suppose and the apparent feeling of the map is like they are stitched together (Having to explain in this manner since I am not able to upload an Image)

I am using OSM, Mapnik(2.3.x branch), ModTile and Renderd.

Also, when I run renderd, I am getting logs like,

renderd[15011]: Rendering projected coordinates 14 4896 6056 -> -8061966.247298|5205055.878110 -8042398.368057|5224623.757351 to a 8 x 8 tile

I have added a layer via layer-shapefile xml as follows,

<Layer name="MS-GIS" status="on" srs="+proj=utm +zone=18 +datum=WGS84 +units=m +no_defs">
    <StyleName>raster</StyleName>
    <Datasource>
      <Parameter name="type">pgraster</Parameter>
      <Parameter name="table">ms_test</Parameter>
      <Parameter name="raster_field">rast</Parameter>
      <Parameter name="dbname">gis</Parameter>
      <Parameter name="estimate_extent">false</Parameter>
      <Parameter name="extent">-20037508,-19929239,20037508,19929239</Parameter>
    </Datasource>
</Layer>

How can get the tiling to be smooth without boundaries? Any help greatly appreciated.