Domain not updated on zoom_onzoomend callback (only when zoom out)

Hello, I implemented a onzoomend callback function that is working fine only when zooming in, the domain parameter updates accordingly. But the problem is when I zoom out, the domain doesn't update anymore.

EDIT: here is a a jsfiddle to show what I'm trying to do and the problem with zooming out: http://jsfiddle.net/b8Lyxp85/