Strange Behaviour on Window Close

I have a panel with multiple sliders that, when used, issue a command to control a Xenon lamp. The widget should be spawned & closed from a button press on another GUI (via Execute "panelName()"), however, when closing this widget with the standard Windows X button every SliderControl's function is called. This is very strange and unwanted behavior. No where in my code do I have any hook on a Windows exit so I wonder if this has happened before? And Is there a way to disable the native Windows option menu or catch the termination to abort these function calls?

Here's a sample SliderControl function to set the lamp intensity:

Function solarSimIntensitySliderProc(sa) : SliderControl
 
    STRUCT WMSliderAction &sa
    NVAR instr = $GLOBAL_PATH + ":ShutterController:SC_solarSim_instr"
    String cmd = ""
    Variable curVal 
 
    switch ( sa.eventCode )
        default:
            if ( sa.eventCode & 1)
                curVal = sa.curval
                sprintf cmd, "P=%04g\r", (curVal * 10)
                HW_SendVISACommand(instr, cmd)
            endif
            break
    endswitch
    return 0
End

Any insight would be greatly appreciated.