The question has already been answered, but since this question do not bring up the question of responsive sites I would like to add some information on that.
I encountered this issue in Chrome on android when developing a responsive web site. When resizing the window I want to hide the menus (due to some design elements needing proper positioning) but the Chrome for android behaviour to trigger a resize event on scroll made that somewhat difficult..
Switching to start using onOrientationChange was not an option since this is a responsive site, there is no orientation change on a desktop PC, but I still needed the code to work on both regular PC:s, tablets and smartphones.
I could had started to do browser sniffing and such but I have so far been able to avoid that..
I tried to implement the solution suggested by CWitty but since scrolling up or down in fact triggers a height-change that did not work either.
I ended up adding a condition that only hides the menu when the width is changed, not when the height has changed. This works in my case since I only need to rewrite the menu when the width is changed.
Just for curiosity, I was trying to reproduce it and if I'm correct this is caused by the navigation chrome bar.
When you scroll down and chrome hides the browser navigation bar it produces a window resize, but this is correct, because after that we have a bigger window size due to the free space that the browser nav bar has left.
Browsers in mobile devices often hide their horizontal top navigation bar when someone scrolls down, and show it again when scrolling up. This behavior affects the size of the client, firing the resize event. You just need to control not executing your code because of height changes or, at least, because of that height change.