jQuery $(window).resize() not working when decreasing window's height

I have a div with an id "main", I want to set its height using jQuery and making so that on window.resize its height is modified using a function but for some reason it works well only when increasing window's height, when decreasing it it doesn't work.

This is the JS:

function setMainH() {

    var docH = $(document).height();

    $("#main").height(docH - 40);

}



$(function() {

    setMainH();

});



$(window).resize(function() {

    setMainH();

});

EDIT: the problem appears either increasing or decreasing

EDIT 2: the resize() event seem to be called correctly, I've tried with

console.log("resizing");

on resizing and it logs correctly so the problem isn't that.