transform node Problem

I use the version 1.03 and create a worldpos node , connect xyz port to transform world2local,
then  get this code,
float3 node_6534 = mul( _World2Object, float4(mul(_Object2World, v.vertex).rgb,0) ).xyz;

transform not support vector4, why not this code:

float4 node_6534 = mul( _World2Object, mul(_Object2World, v.vertex));

transform with the homogeneous coordinates.