JIRA.Events.ISSUE_REFRESHED is triggered twice when the second time view an issue in list

I add a panel to issue screen.
Everything went well, but when I click one issue the second/third time in list, myfunction trigger twice, because JIRA.Events.ISSUE_REFRESHED event is triggered twice.

Events.bind(Types.ISSUE_REFRESHED, function() {
            myfunction();
});

This will cause performance problems.
Have a workaround for the problem?

Thanks in advance