QUESTION ON SEQUENCE VALUES - 9iR2

Web based app (using mod_plsql)

At the start of processing, an activity ID is retrieved from a sequence:

select act_s.nextval
into l_act_id
from dual;

This value is then used as part of an insert statement to log the start of a procedure's execution.

At the end, this code is executed:

select act_s.currval
into l_act_id
from dual;

and then an update statement is executed to update the row whose pk is l_act_id.

The question is this: are there *any* circumstances (that anyone has heard of or come across) where the value returned by the 2nd select would not be the same value as returned by the first?

This is the same sessionid and, as far as I know, the package state (all packages used) is automatically reset at the end of each execution.

Appreciate any thoughts

-- 
jeremy