The zoom stickyness is on the known issues list http://www.waze.com/wiki/index.php/Waze ... and_Issues
How far it zooms out is based on your settings, which can either be for next turn, or based on speed (and next turn). Suspect that you have next turn turned on, which can be a long way depending on your navigation route. Speed will zoom out based on speed, but no further than the next turn.
Also note, that either of these modes can cause the road your are on to disappear if it is not a primary or higher type, are far out zoom levels, unless you have navigation highlighting the road to be used.