trying to analyze deadlock

Hi all,
I'm trying to analyze a deadlock that I have in one of our environments.
The deadlock message :

06:15:49 EET db 14563 DETAIL: Process 14563 waits for ShareLock on
transaction 1017405468; blocked by process 36589.
Process 36589 waits for ShareLock on transaction 1017403840; blocked by
process 14563.
Process 14563: delete from tableB where a in (select id from tableA where c
in (....)
Process 36589: delete from tableA where c in (....)
06:15:49 EET db 14563 HINT: See server log for query details.
06:15:49 EET db 14563 STATEMENT: delete from tableB where a in (select id
from tableA where c in (....)
06:15:49 EET db 36589 LOG: process 36589 acquired ShareLock on
transaction 1017403840 after 1110158.778 ms
06:15:49 EET db 36589 STATEMENT: delete from tableA where c in (....)
06:15:49 EET db 36589 LOG: duration: 1110299.539 ms execute <unnamed>:
delete from tableA where c in (...)

tableA : (id int, c int references c(id))
tableB : (id int, a int references a(id) on delete cascade)
tableC(id int...)

One A can have Many B`s connected to (One A to Many B).

deadlock_timeout is set to 5s.

Now I'm trying to understand what might cause this deadlock. I think that
its related to the foreign keys... I tried to do a simulation in my env :

transaction 1 :
delete from a;
<left in the background, no commit yet >

transaction 2 :
delete from b;

but I couldnt recreate the deadlock, I only had some raw exclusive locks :

postgres=# select
locktype,relation::regclass,page,tuple,virtualxid,transactionid,virtualtransaction,mode,granted
from pg_locks where database=12870;
locktype | relation | page | tuple | virtualxid | transactionid |
virtualtransaction | mode | granted
----------+----------+------+-------+------------+---------------+--------------------+------------------+---------
relation | b | | | | |
51/156937 | RowExclusiveLock | t
relation | a_a_idx | | | | |
51/156937 | RowExclusiveLock | t
relation | a | | | | |
51/156937 | RowExclusiveLock | t
relation | pg_locks | | | | |
53/39101 | AccessShareLock | t
relation | a_a_idx | | | | |
52/29801 | AccessShareLock | t
relation | a | | | | |
52/29801 | AccessShareLock | t
relation | b | | | | |
52/29801 | RowExclusiveLock | t
tuple | b | 0 | 1 | | |
51/156937 | ExclusiveLock | t
(8 rows)

What do you guys think ?