After retrieving a placeholder, the file is blocked

We encountered the following problem with FSA EV 8.0 SP3: 

- A user retrieves an excel placeholder. The user close the file once opened. 
- The placeholder is missing and now we have the original xls. All ok.
- Now, If the user try to rename or delete the xls file, Windows reports a message saying that is in use. 
- After a while, it is possible rename or delete the file. 
- The user has Windows 7. 
- Does not always happen.

Does anyone know what could be the reason? 

Thanks and regards.