[vtkusers] __after_morecore_hook crash

[tom fogal]

Hi all, I'm seeing a segfault in __after_morecore_hook which eventually
leads back up to me deleting a vtkExtractGeometry object.

The crash actually comes from a line in vtkSource::UnRegister line 808
of the implementation:

 if (this->Outputs[idx]->GetNetReferenceCount() != 1)

I'm using the RectilinearGridOutput of a
vtkInterpolateDataSetAttributes as the input:

 this->Extract->SetInput(this->Interp->GetRectilinearGridOutput());

when I use it, as well as an implicit function of a sphere, if that
matters. I suspect it might because I tried a simple test program that
just allocates and deallocates the object, which worked fine.

Any ideas / thoughts on what I might be doing wrong or whats going on?
This is with vtk4.4

Thanks,

-tom