lead() with arrays - strange behaviour

[Thomas Kellerer <spam_eater@xxxxxxx>]

Consider the following dummy table (this is a simplified example from a bigger query):

    create table sample_data (id int, id_list int[]);
    insert into sample_data (id, id_list)
    values 
       (1, array[1,2,3]),
       (2, array[2,3,4]),
       (3, array[4,5,6]);

The following statement tries to find the overlapping values in id_list between the current row and the next row:

    select id, 
           id_list,
           lead(id_list) over (order by id) as next_list,
           array(select unnest(id_list) intersect select unnest(lead(id_list) over (order by id))) as common_ids
    from sample_data;       

The above returns: 

    id | id_list | next_list | common_ids
    ---+---------+-----------+-----------
     1 | {1,2,3} | {2,3,4}   | {}        
     2 | {2,3,4} | {4,5,6}   | {}        
     3 | {4,5,6} |           | {}        

The empty array for "common_ids" is obviously incorrect. 

However, when the evaluation of the "next_list" is put into a derived table, then this works as expected:

    select id, id_list, next_list, 
           array(select unnest(id_list) intersect select unnest(next_list)) as common_ids
    from (
      select id, 
             id_list,
             lead(id_list) over (order by id) as next_list
      from sample_data
    ) t

returns:

    id | id_list | next_list | common_ids
    ---+---------+-----------+-----------
     1 | {1,2,3} | {2,3,4}   | {2,3}     
     2 | {2,3,4} | {4,5,6}   | {4}       
     3 | {4,5,6} |           | {}        

This is with Postgres 11.4

Is this a bug or simply not supported?

It does work correctly with intarray's "intersect" operator:

    select id, 
           id_list,
           id_list & lead(id_list) over (order by id) as next_list
    from sample_data;       


However, the actual data uses a bigint, so intarray isn't an option.

Thomas