That's right.
We are also thinking how to do this kind of processes, but we also want to keep log what was changes, so we don't mind multiple same task.
Eg. node1 set to value A, then rejected, node1 set to value B, again rejected, node1 set to C and accepted. Process finished.
Then the history show what was changed when, which is ok for us:
user X set value A on 1.1.2011
reject by Z on 1.1.2011
user X set value B on 2.1.2011
rejected by Z on 2.1.2011
user X set value C on 3.1.2011
accepted by Z on 3.1.2011
I think there is no posibility to open same instance of task - which would mean change of status from Completed to Ready.
Let us know if you find some nice solution.