TRUNCATE TABLE giving error even with DROP ANY TABLE system privilege

Hi

I have a table called TEST1.T1:

create table test1.t1 (id int, constraint pk_id primary key(id));

and another called TEST1.T2:

create table test1.t2 (id int, constraint fk_id foreign key(id) references test1.t1(id) on delete cascade);

I have created a stored procedure in another schema TEST2.TPROC

create or replace procedure test2.tproc as

begin

execute immediate 'TRUNCATE TABLE TEST1.T1 CASCADE';

end tproc;

My user id is smitra and I have granted execute role to the user on this procedure:

grant execute on test2.tproc to smitra;

I also granted DROP ANY TABLE TEST2 user:

grant drop any table to test2;

When I execute this SP:

exec test2.tproc;

I get error:

BEGIN test2.tproc; END;

ERROR at line 1:

ORA-01031: insufficient privileges

ORA-06512: at "TEST2.TPROC", line 4

ORA-06512: at line 1

My question is when the TEST2 user, in which the procedure is defined, has the DROP ANY TABLE system privilege why it's throwing this error?

The only I was able to resolve the error is to change the DEFINER RIGHTS of the SP to INVOKER RIGHTS. Can somebody please explain why I am getting this error? I am using Oracle 12.1