Window randomly gets focus

Hello,

I've made simply script which sends key to a window which works fine... but window sometimes gets focus (window is a full screen app, so it maximizes, which is annoying). Do you have any idea why this happenes and how can I prevent it?

HotkeySet("{NUMPADADD}","StartPause1")
$pause1=False
While 1
Sleep(1000)
WEnd

Func Startpause1()
$pause1=Not $pause1
While $Pause1=True
Sleep(1000)
ControlSend ( "XXX", "", "", "9")
Sleep(10000)
WEnd
EndFunc

Thanks in advance,

Sloniu