A Validation Error resfreshes the page and JavaScript won't execute. Why?

I use this code in JavaScript to hide the PreviousButton on a page:

Qualtrics.SurveyEngine.addOnload(function() {
jQuery("input#PreviousButton.PreviousButton.Button").css("display", "none");
});

I use this code on the first question of the block, no page break, and put it in addOnload, addOnready, addOnunload.

However, one of the question has a validation parameter. When this validation is not met and the NextButton is pressed, the page reloads and the PreviousButton is back.

Why is that so and how to fix it?