Marauder's Map Folly?

[Rachel Crofut]

No: HPFGUIDX 150766

In Prisoner of Azkaban, Harry, Ron, and Hermione go to see Hagrid before 
Buckbeak's execution.  While they are in his hut, Ron finds Scabbers (a.k.a. 
Peter Pettigrew).  Lupin becomes aware of the fact that Pettigrew is still 
alive based on the Marauder's Map he is looking at at the time.

My question is - when Harry and Hermione use the Time-Turner to save 
Buckbeak and Sirius, why does Lupin not see two Harrys and two Hermiones?  
Snape as well does not notice this when he arrives to give Lupin his potion 
and sees the map.  Is there any explanation for this?

~ Rachel