If we do not do this, then every time we instantiate a new map using the same div, the clientHeight as reported by the browser grows, and eventually we're doing tests with a totally different sized window than we intended to. git-svn-id: http://svn.openlayers.org/trunk/openlayers@5457 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf