Switch / Action ports do not create new signals each time a new sample is processed through them. Any one branch is turned on or off, but remains that way until it is changed. So you have one signal transition when flg is 1, and another when flg first becomes 0 -- but then it stays that way with the 0s that follow.
Think of it as being like an on/off switch. The switch is turned on with the first 1, and then it stays on until the time of the first 0, at which point it is turned off. And it then stays off. The switch is not effectively reversed on at each candidate time: if the input value does not change, there is no transition.
