There's work around for this, however it is annoying:

// Workaround for gcc/msvc where passing small mono structures by value does not work
CUSTOM private static void Internal_GetTexelSize (Texture tex, out Vector2 output)
{
Texture& texture = *tex;
output->x = texture.GetTexelSizeX();
output->y = texture.GetTexelSizeY();
}

///*undocumented* Generally used only in image effects...
CSRAW public Vector2 texelSize { get { Vector2 r; Internal_GetTexelSize(this, out r); return r; } }