Visual Studio Compiler warning C4250 ('class1' : inherits 'class2::member' via dominance)

The following code generates warning C4250. My question is, what's the best solution to it?

class A
{
  virtual void func1();
}

class B : public A
{
}

class C : public A
{
  virtual void func1();
}

class D : public B, public C
{
}

int main()
{
  D d;
  d.func1(); // Causes warning
}

According to what I've read it should be possible to do this:

class D : public B, public C
{
  using B::func1();
}

But, this doesn't actually do anything. The way I've currently solved it is:

class D : public B, public C
{
  virtual void func1() { B::func1(); }
}

What's everyone's view on this?