Minuteur (egg timer app) script: need system events help

I’m very new to applescript, but I tried to make the code as clear as possible.
Basically, Minuteur is a egg timer application, and has a full screen timer mode. I want to make a script that turns on full screen mode,
starts a countdown (time for working), and after that ends, turn off full screen mode and start another countdown (break time).

The problem is, the second time the full_screen() function is called, there’s a system beep to signal an illegal keystroke and nothing happens. If its at all obvious, what am I doing wrong here? Thanks in advance for any help.


-- string is in "hhmmss" format
set _duration to "000010"
set _duration_as_int to 10
set _break to "000010"
set _break_as_int to 10

tell application "Minuteur"
	activate
end tell

full_screen()

-- start work countdown
tell application "Minuteur"
	StartCountdown _duration
end tell

-- turn off full screen 3 seconds before alarm rings
delay (_duration_as_int - 3)

full_screen()

-- after alarm ends, let ring for 3 seconds
delay 6

-- start break countdown
tell application "Minuteur"
	StartCountdown _break
end tell

-- let ring for 3 seconds
delay (_break_as_int + 3)

-- pause the timer
tell application "Minuteur"
	Pause
end tell

-- pressing cmd-f in Minuteur toggles full screen view
on full_screen()
	tell application "System Events"
		keystroke "f" using command down
	end tell
end full_screen

Having downloaded it and played with it, the difficulty seems to be that Mineteur won’t respond to escape or command-f unless the full screen window is first clicked. None of the tricks I tried would bring it frontmost from a script so it would “listen” to keystroke “f” using command down, or key code 27 [escape].