When clicking the "x" button at the right top of the browser, it throws java.lang.IllegalStateException

Testsuite: set2 in applet
Test name(s): set2/dropbox_RockPaperScissors
Product(s) tested: Jre7u91b10 32bit
OS/architecture:win8.1-x64
Reproducible: Always
Reproducible on machine: egtc

Is it a Regression: NO

Test result on the last GAed release for this train:
Win8.1-x64-JDK7u85b15-32bit-IE11:fail

[if Fail] Test result on FCS:
Win8.1-x64-JDK1.7.0b147-32bit-IE11:fail

Is it a platform specific issue:
Mac10.11-x86_x64-jdk7u91b10-64bit-FF40: Failed as the same issue.

Exception/Error from Log:http://aurora-ds3.us.oracle.com:9502/runs/01095/1095259.ManualSubmit/1095259.ManualSubmit-1/workDir/set2/dropbox_RockPaperScissors.jtr

Copy applet workspace,install test jre,and run this case

Test Procedure:
1. Go to Java Control Panel / Security, add https://dl.dropboxusercontent.com to ESL
2. Browse http://dl.dropbox.com/u/44303246/Games/Rock-Paper-Scissors/bin/Index.html
3. Press Space to begin
4. Select game mode
5. Play the game, attempt to test applet functionality
6. Try to resize the applet, browser window
7. Check the Java Console for warnings, errors
8. Close all browser/applet windows to terminate the applet

The actual result:
When clicking the "x" button at the right top of the browser,it throws java.lang.IllegalStateException. Please refer to attach

verification:
win8.1-x64-jdk7u91b09-32bit-IE11:failed as the same issue
win8.1-x64-jdk7u91b05-32bit-IE11:failed as the same issue
win7-x86-jdk7u91b10-32bit-IE9:failed as the same issue