[Chameleon] libpng warning

[Ken-ichi]

Hi all,

My Chameleon app is generating a whole lot of warnings in Apache's 
error_log file, and they look like this:

libpng warning: tRNS chunk not allowed with alpha channel

Actually, about 140 lines of that per page load.  This is on a machine 
running Mapserver 4.8.1, PHP 5.0.5, Apache 2.0.55, and Chameleon 2.2.  
Here's a mapfile that will cause the error:

MAP
    NAME "test"
    STATUS ON
    EXTENT -363827 -615083 548549 481459
    SIZE 410 500
    SHAPEPATH "/path/to/data/"
    SYMBOLSET "/path/to/symbols.sym"
    FONTSET "/path/to/fonts.txt"
    UNITS METERS
    WEB
        IMAGEPATH "/path/to/ms_tmp/"
        IMAGEURL "/ms_tmp/"
    END

    PROJECTION
        "proj=aea"
        "ellps=clrk66"
        "datum=NAD27"
        "lon_0=-120"
        "lat_1=34"
        "lat_2=40.5"
        "x_0=0"
        "y_0=-4000000"
        "units=m"
    END
    OUTPUTFORMAT
        NAME "png"
        MIMETYPE "image/png"
        DRIVER "GD/PNG"
        EXTENSION "png"
        IMAGEMODE RGB
    END

    LAYER
        NAME "Water"
        GROUP "hidden"
        METADATA
          "legendvis"  "hidden"
        END
        STATUS DEFAULT
        DATA "water"
        TYPE POLYGON
        PROJECTION
            "proj=aea"
            "ellps=clrk66"
            "datum=NAD27"
            "lon_0=-120"
            "lat_1=34"
            "lat_2=40.5"
            "x_0=0"
            "y_0=-4000000"
            "units=m"
        END
        CLASS
            STYLE
                COLOR 178 214 214
            END
        END
    END
END


I've tested this with the CGI and with a simple, non-Chameleon PHP 
mapscript app and neither of those generate this error.  Note that these 
warnings don't seem to have any effect on the Chameleon app itself, they 
just fill up the log file.

Has anyone seen this error before, or have any clue as to what might be 
going on?

-Ken-ichi