Thank you Jawahar.
After reviewed entire SAP notes release for SP6 and found following two notes number. But both notes does not saying, once close the browser the session would automatically closed.
https://websmp202.sap-ag.de/~sapidb/012002523100011868192015E
2153824 - The sessions created when viewing crystal reports using URL reporting do not get cleared after session timeout
2237872 - CMS sessions are not released for browser close