GFX:Depth replacement bug?

I’m using a GFX5200(56.72).I wrote a little depth-replace shader.It consists only of the line gl_FragDepth=0.2;
The shader compiles and links properly,but my app is not working as i expected.I checked the assembly output and I see:
MOVR o[DEPR].z, {0, 0, 0, 0}.x;
I’m wondering if anyone has encountered this.Is it a bug and,if yes,will it be fixed with future drivers?