I ran a quick test and can't reproduce using the code below.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=7,IE=9" />
<!--The viewport meta tag is used to improve the presentation and behavior of the samples
on iOS devices-->
<meta name="viewport" content="initial-scale=1, maximum-scale=1,user-scalable=no"/>
<title>
Simple Image Service
</title>
<link rel="stylesheet" type="text/css" href="http://serverapi.arcgisonline.com/jsapi/arcgis/2.8/js/dojo/dijit/themes/claro/claro.css">
<style>
html, body { height: 100%; width: 100%; margin: 0; padding: 0; }
</style>
<script type="text/javascript">
var djConfig = {
parseOnLoad: true
};
</script>
<script type="text/javascript" src="http://serverapi.arcgisonline.com/jsapi/arcgis/?v=2.8">
</script>
<script type="text/javascript">
dojo.require("dijit.layout.BorderContainer");
dojo.require("dijit.layout.ContentPane");
dojo.require("esri.map");
var map;
function init() {
var initExtent = new esri.geometry.Extent({
"xmin": -13409020.592351478,
"ymin": 5800583.682038919,
"xmax": -13259815.513138756,
"ymax": 5885581.657492069,
"spatialReference": {
"wkid": 102100
}
});
map = new esri.Map("map", {
extent: initExtent
});
var basemap = new esri.layers.ArcGISTiledMapServiceLayer("http://server.arcgisonline.com/ArcGIS/rest/services/World_Topo_Map/MapServer");
var params = new esri.layers.ImageServiceParameters();
params.noData = 0;
var imageServiceLayer = new esri.layers.ArcGISImageServiceLayer("http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Portland/CascadeLandsat/ImageServer", {
id:"cascadeLandsat",
imageServiceParameters: params
});
map.addLayer(basemap);
map.addLayer(imageServiceLayer);
dojo.connect(map, 'onLoad', function(theMap) {
//resize the map when the browser resizes
dojo.connect(dijit.byId('map'), 'resize', map,map.resize);
});
}
function removeLayer(){
var imageLayer = map.getLayer('cascadeLandsat');
map.removeLayer(imageLayer);
}
dojo.addOnLoad(init);
</script>
</head>
<body class="claro">
<div dojotype="dijit.layout.BorderContainer" design="headline" gutters="false"
style="width: 100%; height: 100%; margin: 0;">
<div dojotype='dijit.layout.ContentPane' region='top' style='height:20px;'>
<input type='button' value='Click' onclick='removeLayer();'/>
</div>
<div id="map" dojotype="dijit.layout.ContentPane" region="center" style="overflow:hidden;">
</div>
</div>
</body>
</html>