update_struct

Hi,

The following gives an error for both (uncommented) update_struct
calls:


	:- local struct( sub(d, e) ).
	:- local struct( a(b, c:sub) ).

	:-	X = a with [b:1, c:Xc],
		Xc = sub with [d:2, e:3],

	%	update_struct(a, [d:20], Y, Z).
	%	update_struct(a, [c:C], Y, W).



so: does update_struct only work with unnested structures?
It is not mentioned in the documentation...

Cheers,
Sebastian