Check for ldc.conf next to the ldc binary before home and etc. The new search order is * current working directory * next to executable * user home directory * prefix/etc * prefix/etc/ldc * /etc * /etc/ldc

interface I {}
class A : I {}
class B : A {}

void main () {
    A a = new A;
    I i = a;

    assert(!cast(B)a);
    assert(!cast(B)i);
}