Flash work slow when the page is in background of browser

Question

I'm developing a game during which a clock which states that every three seconds a soldier will be added to the screen , and another clock that moves the soldier from the left to the right side of screen every 20 milliseconds .
Everything works correctly, until the game rises locate the air. If the user chooses to leave the game for a few minutes and messing with another page in browser , the watches of the Flash game starts to work very slow , which is why the soldiers are moving at low speed and thus accumulate masses of soldiers on screen, while they were supposed to be gone long .
I'm trying to create a " self timer " , instead of dealing with flash clock ( Timer ) , but I got involved with recursion fills the cartridge and creates StackOverFlow error.
I can not use the event Event.ENTER_FRAME etc. , because also this event work slow when the game is in the background
What to do ? Who can help me?

Answer 1

Thank you!
I solved it, similar to what you suggested, through the ACTIVATE event is linked to the stage.  That:
                    private function stageDeactivate(e:Event)
                              if (stage != null)
                                        stage.removeEventListener(Event.DEACTIVATE, stageDeactivate);
                                        stage.addEventListener(Event.ACTIVATE, stageActivate);
                                        stopSoldiers();
                    private function stageActivate(e:Event)
                              if (stage != null)
                                        stage.removeEventListener(Event.ACTIVATE, stageActivate);
                                        stage.addEventListener(Event.DEACTIVATE, stageDeactivate);
                                        playSoldiers();