CanvasItem based FormItem's as Custom Filter Editor not compatible with Frozen header

[alu]

This is a very strange but serious problem we've been experiencing...
When we initialized a listgrid with one or more frozen fields as well as showFilterEditor:true, everything appeared to work well. Then I decided to unfreeze a column, and suddenly all filterEditor fields that are based on CanvasItem becomes blank (darkgrey), while adding previously hidden ones that are also based canvasitem is fine...
After some investigation, I am now able to isolate this issue with a simple test case

isc.DataSource.create({
    ID: "countryDS",
    fields:[
        {name:"countryName", frozen:true, type:"text", title:"Country"},
        {name:"countryCode", type:"text", title:"Code"},
        {name:"independence", title:"Independence", type:"dateTime"},
        {name:"population", title:"Population", type:"integer"},
        {name:"gdp", title:"GDP ($B)", type:"float"}
    ],
    clientOnly: true
});

isc.ListGrid.create({
    ID: "countryList",
    width:500, top:50, alternateRecordStyles:true,
    dataSource: countryDS,
    autoFetchData: true,
    autoFitData: "vertical",
    showFilterEditor: true,
    getFilterEditorType:function(aInField_o)
    {
    	if(aInField_o.type === "integer")
	{
		return "ButtonItem";
	}
	else
	{
	    return this.Super("getFilterEditorType", arguments);
	}
    },
    autoFitMaxRecords: 10
});

Now if you unfreeze the countryName, the population filterHeader(a ButtonItem just for simplification) will get greyed out.
This is reproducible on latest showcase. We have purchased basic support.

[Isomorphic]

Thanks for the clear test case. We've made a change to address this issue in the 9.0p and 9.1d branches.
This will be available tomorrow - build dated Dec 5 or above

Regards
Isomorphic Software