Bandbox popup doesn't close when it lose focus

Steps to Reproduce

1. load the zul t5824.zul
2. click "open" button
there are lots of bandbox in a large grid.
3. scroll down to the last row
4. click to open bandbox popup in the last row
5. click the last row to make bandbox popup lose focus

Current Result

the bandbox popup doesn't close

Expected Result

the bandbox popup close itself

Debug Information

• the modal window must be high enough to contribute a vertical scrollbar, this bug happens.
  after you open the last bandbox popup in the last row, if you click the previous row, the bandbox popup will close

Workaround