The following two files generate an access violation in dmd.exe on my machine:

file a.d:
interface I
{
void method();
}
class A : I
{
void method()
{
}
}
class B : A
{
void method()
{
}
}

file c.d:
import a;
class C : B
{
}
void main()
{
C c = new C;
}

Build command line:
dmd -c a.d
dmd c.d a.obj

Notes: Moving class B from file a.d into c.d removes the access violation, as well as removing the interface (as well as references to the interface of course).

I am running WinXP Home Edition.