ndicki, I found the same issue. Must be a missing texture. I went back to the old suneffect.xml. If anyone has an answer I would like to use any new effects but as of now the sun is square.
Cheers Tom. Glad to know I'm not going funny...
I've checked suneffect.xml and found this:
<SunGlare Size="2.5" Location="1.00" Intensity="0.4" Red="255" Green="255" Blue="204" Texture=
"sun_glare_d.dds" u1="0.0" v1="0.0" u2="1.0" v2="1.0" UpAlign="1"/>
<SunGlare Size="0.075" Location="0.75" Intensity="0.20" Red="255" Green="0" Blue="255" Texture=
"sun_glare_d.dds" u1="0.0" v1="0.0" u2="1.0" v2="1.0" UpAlign="1"/>
<SunGlare Size="0.0625" Location="0.70" Intensity="0.20" Red="0" Green="0" Blue="255" Texture=
"sun_glare_c.dds" u1="0.0" v1="0.0" u2="1.0" v2="1.0" UpAlign="1"/>
<SunGlare Size="0.050" Location="0.65" Intensity="0.20" Red="0" Green="255" Blue="0" Texture=
"sun_glare_b.dds" u1="0.0" v1="0.0" u2="1.0" v2="1.0" UpAlign="1"/>
<SunGlare Size="0.0375" Location="0.60" Intensity="0.20" Red="255" Green="0" Blue="0" Texture=
"sun_glare_a.dds" u1="0.0" v1="0.0" u2="1.0" v2="1.0" UpAlign="1"/>
<SunImage Texture=
"sun_main.dds" Size="0.02" BlendMode="1"/>
<Corona Texture=
"sun_corona_d.dds" Size="0.0225" BlendMode="1" UpAlign="1"/>
The image files highlighted in red appear to be missing from the package.