what is not normal is the output of the op-amp when fed up with the signal from X1.

That is the opposite of what you said in your original post.

but when connected, the output of the op amp is ok, but the signal voltage goes bellow -400v and over +400v peak to peak

 

That is the opposite of what you said in your original post.

those are two statements about two different tests.
There are three situations here:
1- signal from X1 has a fixed amplitude that goes to the op-amp. the op-amp gives a 5v square wave.
2- signal from X1 has an amplitude that increases over time, and the op-amp gives a normal 5v square wave. what is not normal is that the signal from X1 should only go to about 2v pk-to-pk but instead it goes beyond 800v pk-to-pk.
3- signal from X1 has an amplitude that increases over time to some limit and then it decreases back to 0v but when connected to the op-amp the signal from X1 becomes incorrect and i get a weird signal from the op-amp.

all the images are in the first post.

 

those are two statements about two different tests.
There are three situations here:
1- signal from X1 has a fixed amplitude that goes to the op-amp. the op-amp gives a 5v square wave.
2- signal from X1 has an amplitude that increases over time, and the op-amp gives a normal 5v square wave. what is not normal is that the signal from X1 should only go to about 2v pk-to-pk but instead it goes beyond 800v pk-to-pk.
3- signal from X1 has an amplitude that increases over time to some limit and then it decreases back to 0v but when connected to the op-amp the signal from X1 becomes incorrect and i get a weird signal from the op-amp.

all the images are in the first post.

Twice, you said it as the X1 signal that was wrong.