difference between a imported namespace and a declared one

this code work well:

#ns {
.nsmixin(@color){
color: @color;
}
}

.mixin()
{
.test2 {
        #ns > .nsmixin(blue);
}
}
.mixin();

Then i create a file ns.less which contains:

.nsmixin(@color){
color: @color;
}

now the code below shows an error:

#ns { @import "ns.less";}

.mixin()
{
.test2 {
        #ns > .nsmixin(blue);
}
}
.mixin()

error: "SyntaxError: #ns > .nsmixin is undefined" this only happens when its wrapped inside a mixin. Use the namespace in a class works well too:

   #ns { @import "ns.less";}
   .test2 {
        #ns > .nsmixin(blue);
    }

Reproduce the two namespace examples and compare declared versus imported namespaces, especially when the namespace is referenced inside a mixin. The payload names no source files or tests, so first locate the namespace and import-resolution code and any existing regression tests. Done means the behavior is fixed consistently or the supported difference is clearly documented.