Holding a value for a specific time with zero order hold block in Simulink

I want to hold the newest peak (the last peak – input changing from 0 to 1) for an hour. I used the zero order hold Block for that purpose (sample time 3600s). But the problem with zero order hold block is, it sometimes omits the peak and I am not getting why it does that.

As you see in the attached picture, the blue line is the held curve and the red one is the input. One can see that, in the places where I marked wrong, the peak is not held as wanted it to.

Anybody has experience with this matter?