[OpenLayers-Users] Context is undefined and missing part of feature

[emmexx]

I'm having some trouble using a Vector layer and the
addUniqueValueRules() function.

I create an array of vector layers and define a lookup rule to style
some feature (lines).

var myStyles = new OpenLayers.StyleMap({
	"default": new OpenLayers.Style(null, {
		rules: [
			new OpenLayers.Rule({
				symbolizer: {
				"Point": {
					pointRadius: 5,
					graphicName: "square",
					fillColor: "white",
					fillOpacity: 0.25,
					strokeWidth: 1,
					strokeOpacity: 1,
					strokeColor: '#' + color,
				},
				"Line": {
					strokeDashstyle: ol_dash,
					strokeWidth: 5,
					strokeOpacity: 1,
					fillColor: "white",
					strokeColor: '#' + color,
					label: mylabel,
					labelAlign: "rm",
					fontSize: "12px",
					fontWeight: "bold",
					fontColor: '#' + label							}
			}
		})
		]
	})
});
myStyles.addUniqueValueRules("default", "attr1", attr1);
myStyles.addUniqueValueRules("default", "attr2", attr2);

In another layer I load a gpx file:

vlayer2= new OpenLayers.Layer.GML("gps", path,
{
	format: filetype
	formatOptions: {
		extractAttributes: false,
		extractStyles: false,
		maxDepth: 2,
		extractTracks: true,
		extractRoutes: false,
		extractWaypoints: false
	},
	'styleMap': styleMap,
	projection: map.displayProjection
});

If gpx line is outside the visible map I drag the map but the line is
not "refreshed" and the previously hidden part is not visible. I have
to, for example, zoom in and out to get the line visible.

If I comment out the 2 addUniqueValueRules lines the problem disappear.
No problem also if I debug the code in Firebug and put a breakpoint on
one of those 2 lines.

After dragging the map in ff error console I find:
context is undefined
.../Openlayers-2.8/Openlayers.js Line 1423.

Any suggestion?

Thank you
	maxx

p.s. I cut the unnecessary code