SQL & PL/SQL

This thread is continued from 1056886
and 1057057

select * from v$version;

BANNER
-------------------------------------------------------
Oracle Database 11g Release 11.2.0.1.0 - Production
PL/SQL Release 11.2.0.1.0 - Production
CORE    11.2.0.1.0      Production
TNS for 32-bit Windows: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production

create table siblingsT(
ID    number primary key,
OyaID number);

insert into siblingsT values(1,null);
insert into siblingsT values(3,   1);
insert into siblingsT values(5,   3);
commit;

select connect_by_root ID as treeID,ID,OyaID
  from siblingsT
start with OyaID is null
connect by prior ID = OyaID;

treeID  ID  OyaID
------  --  -----
     1   1   null
     1   3      1
     1   5      3

OK I will emulate connect_by_root in recursive with clause :-)

with rec(treeID,ID,OyaID) as(
select ID,ID,OyaID
  from siblingsT
 where OyaID is null
union all
select a.ID,b.ID,b.OyaID
  from rec a,siblingsT b
 where a.ID = b.OyaID)
select * from rec;

treeID  ID  OyaID
------  --  -----
     1   1   null
     1   3      1
     3   5      3

But I think correct result is below :-(
Why treeID of third row is 3 ?

treeID  ID  OyaID
------  --  -----
     1   1   null
     1   3      1
     1   5      3

****************************************************************************************************
SomeHow below SQL which exchange a.ID to a.TreeID returns correct result.
But I think this is a bug B-)

with rec(treeID,ID,OyaID) as(
select ID,ID,OyaID
  from siblingsT
 where OyaID is null
union all
select a.treeID,b.ID,b.OyaID
  from rec a,siblingsT b
 where a.ID = b.OyaID)
select * from rec;

treeID  ID  OyaID
------  --  -----
     1   1   null
     1   3      1
     1   5      3