Improper extension errors in shader window

[paulhilbert]

When (for example?) enabling EXT_frag_depth in host code and adding:

#extension GL_EXT_frag_depth : enable
//...
void main() {
    //...
    gl_FragDepthEXT = gl_FragCoord.z;
}

The fragment code window is in error display mode ("undefined variable gl_FragDepthEXT") despite correctly compiling, executing and rendering.