If this is the calculation you use for instancing:
gl_Position = p3d_ModelViewProjectionMatrix * (p3d_Vertex * transform);
And this is the calculation we use for animating a model:
gl_Position = p3d_ModelViewProjectionMatrix * matrix * p3d_Vertex;
Then this would be the calculation to use for instancing the animated model:
gl_Position = p3d_ModelViewProjectionMatrix * ((matrix * p3d_Vertex) * transform);