Strange procedure executions, and dbms_lock.sleep(7)

I had executed a number of procedures (approx. 80) from TOAD as follows:

exec <schema_name>.<procedure name>;

...

exec <schema_name>.<procedure name>;

exec <schema_name>.<procedure name>;

Although it says as:

PL/SQL procedure successfully completed.

It does not. Because the tables that must be accumulated by those procedures are empty. For this reason I tried it in SQL*Plus, but it does not work either. After then, I put the executions of the procedures in a PL/SQL block with dbms_lock.sleep(3) as follows:

begin
<schema_name>.<procedure name>;

dbms_lock.sleep(3);

<schema_name>.<procedure name>;

dbms_lock.sleep(3);

...

<schema_name>.<procedure name>;

 Then it worked!

I amcurrently using, Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit on a ia64 hp server rx4640 box.