Antarctica disappears with Mercator projection

[Ei Fujioka]

Hello experts,

I'm developing an online mapper where you can change the projection.
http://seamap.env.duke.edu/prod/mapservice/onlinemap/oms_main_v2.phtml

The default projection is the geographic WGS84.
You can change this by switching to [OPTIONS] tab and hit [Projection] 
button. In the popup window, if you choose "World Mercator", Antarctica 
disappears.
I tried to change latitude values in EXTENT (e.g. -90, -85, etc.) but 
didn't make difference.

Any idea why this happens and how to work around?

It's an ESRI's shapefile and Antarctica is projected properly in 
Mercator with ArcGIS.

The excerpt from mapfile below.

MAP
   NAME "OBIS MAP"
   UNITS DD
   IMAGETYPE png
   EXTENT -180 -83.6236 180 83.6236
   PROJECTION
     "init=epsg:4326"
   END

   LAYER
     NAME "Continents"
     STATUS DEFAULT
     DATA "countries"
     TYPE POLYGON
     TRANSPARENCY 0
     PROJECTION
       "init=epsg:4326"
     END
     CLASS
       NAME "Countries"
       COLOR 204 204 204
       OUTLINECOLOR 153 153 153
     END
     METADATA
       "wms_abstract" "Countries"
       "TITLE" "Countries"
       "wms_title"  "Countries"
     END
   END
END

Thanks,

Ei

-- 
======================
   Ei Fujioka
   Research Associate
   Duke University

   (919) 613-8021
   efujioka at duke.edu
======================