Why does the signal work like this?

Question

Electronics

Why are the signals different? Could this be a Proteus issue or not?
There are 2 signals FIRE and STAND-BY : Thigh=900ms Tlow=100ms. They are synchronous (since from one CLK).
With the help of a voltage divider (which is on a different circuit; I don’t know if it’s important to show it too) I influence one of the signals.
The voltage starts to change from 5V to 4.99972V.
But the graph shows that in this mode, the STAND-BY input signal drops to 0, and if the divider is turned in the other direction, then the FIRE input signal is constant.
And the problem is that the signal changes states and the counter starts counting, which I do not need.
What is the reason? My mistake or programs?
Yellow signal - FIRE
Blue signal - STAND-BY

Answer 1

Frankly speaking. Proteus is not suitable for modeling analog circuits, to put it mildly. ( feels a touch of déjà vu )

Answer 2

I think you are idealizing the signal too much, in fact it is like this: see fig. From this all the problems