[Tilecache] bad quality with 8bit AGG PNG images and metaTile=true

[Ivan Mincik]

I am using UMN Mapserver WMS server version 5.2.1 which is rendering PNG images using AGG backend. They are reduced to 8bit. 
When the Tilecache option "metaTile" is set to false, I have nice looking tiles. For the layers containing  labeIs I need to use option "metaTile=true".

Using the option "metaTile=true" for 8bit AGG PNG images gets visibly worse looking results. Can it be some problem with combination PIL and reduced 8bit images ?

Tilecache version is 2.03-1.

MapFile options are:

       OUTPUTFORMAT
                NAME "PNG_AGGAQ"
                DRIVER "AGG/PNG"
                MIMETYPE "image/png"
                IMAGEMODE RGBA
                FORMATOPTION "QUANTIZE_FORCE=ON"
                FORMATOPTION "QUANTIZE_DITHER=OFF"
                FORMATOPTION "QUANTIZE_COLORS=256"
                FORMATOPTION  "INTERLACE=OFF"
                TRANSPARENT ON
        END

Tilecache config:
[layername]
type=WMSLayer
url=http://server/cgi-bin/mapserv?map=map.map&transparent=true
layers=layername
extension=png
debug=on
metaTile=true
extent_type=loose
srs=EPSG:2065
bbox=-273393.437500, -1256155.375000, -255811.593750, -1227652.250000
resolutions=176.38879363894028529, 88.19439681947014265, 35.27775872778806132, 17.63887936389403066, 8.81943968194701533, 3.52777587277880578, 1.76388793638940289, 0.88194396819470144, 0.35277758727788061, 0.17638879363894031


Thanks 
Ivan