Problem is caused by not complete "copy" of nod_rse in cmp.cpp.
It may occur in others conditions (not with COMPUTED BY), but it's reproducable with it.
create table t1 (n integer);
create table t2 (n integer, c computed by ((select n from t1)));
insert into t1 values (1);
insert into t1 values (2);
insert into t2 values (1);
-- this select should throw a error since the computed expression returns more than one row
select * from t2;