Spreadsheet doesn't be released after close tab.
steps.
1.open coedit.zul with 2 browser
2.close 1 tab (desktop will be cleanup)
3.dump memory, you will see the spreadsheet in memory is still 2.
4.do some action in another tab.
5.dump memory again, the spreadsheet count reduce to 1.

Issue:
the spreadsheet looks like not remove immediately after desktop remove