Work item still in inbox

[ASSY, SOSTHENE]

Hi every body,
 
I'm using sap 4.7 to  approve my Purchase requisition which has 3 levels
N0, N1, N2.
After n0, the document is sent to the purchasing group chief. He releases
with N1.
When released, the document is sent to Material group manager. He   releases
with N2.
 
 
PB ? when released with N2, the document status changed but the work item is
still in the inbox.
Need Help
 
Thank you for any help