Based on the unophuscated code I attached on CustomEditor thread, the this.OnDropdown function, line #128, will be responsible to show the slidebar and position it on the screen. These are the original lines to position the slidebar:

if (left+width > document.body.offsetWidth)
  ddObj.style.left = left - ((left+width) - document.body.offsetWidth) - 50;

if (top+height > document.body.offsetHeight) {
  var pTop = top - ((top+height) - document.body.offsetHeight) - 20;
  if (pTop < 0) pTop = 25;
  ddObj.style.top = pTop;
}

For example if you wanted to always position the slidebar 10px from the left and top of the page, please modify the line above to these lines:

ddObj.style.left = "10px";
ddObj.style.top = "10px";

Does this issue is reproducable using the supplied WebGrid sample? for example Filtering.aspx and EnableFiltering.aspx

The only way I could reproduce  the issue, the filter image icon will be left aligned, is when we are using XHTML Doctype. WebGrid currently have not fully supported XHTML Doctype. Please use HTML Doctype to solve this issue. 

This issue only occurs if we are using Slidebar in XHTML Doctype page. Currently Slidebar only support HTML Doctype. Please use HTML Doctype if you are using Slidebar custom editor.

Just quoting from my response in Multiple Datakey Fields thread

Inorder to support multiple key field scenario you don't need toset the DataKeyField property in the WebGrid table. We already have a sample of this scenario in HierarchicalGrid.aspx. The OrderDetails has multiply key, OrderID and ProductID, so in the OrderDetails WebGrid definition no DataKeyField property is assigned 

<ISWebGrid:WebGridTable Caption="Order Details" DataMember="Order Details">

On the other hand, the Order table which has the primary key OrderID will have to be assigned the DataKeyField property

<ISWebGrid:WebGridTable Caption="Orders" DataKeyField="OrderID" DataMember="Orders">

In order to define you own column to display you need to implement the PrepareDataBinding event handler and define the WebGrid table column you wish to display. In most of the Intersoft provided sample, the column generation is using RetrieveStructure function to auto generate the column based on the binded data schema.

Here is the snippet to show certain column of the datasource, for this example we would like to show column id, firstname, lastname, and value:

protected void grdObj_PrepareDataBinding(object sender, ISNet.WebUI.WebGrid.DataSourceEventArgs e)
{
    if (!Page.IsPostBack )
    {
        WebGridColumn wgColID = new WebGridColumn();
        wgColID.Caption = "ID";
        wgColID.DataMember = "id";
        wgColID.Name = "id";
        wgColID.Width = Unit.Pixel(150);
        grdObj.RootTable.Columns.Add(wgColID);

        WebGridColumn wgColFirstName = new WebGridColumn();
        wgColFirstName.Caption = "First Name";
        wgColFirstName.DataMember = "firstname";
        wgColFirstName.Name = "firstname";
        wgColFirstName.Width = Unit.Pixel(250);
        grdObj.RootTable.Columns.Add(wgColFirstName);

        WebGridColumn wgColLastName = new WebGridColumn();
        wgColLastName.Caption = "Last Name";
        wgColLastName.DataMember = "lastname";
        wgColLastName.Name = "lastname";
        wgColLastName.Width = Unit.Pixel(250);
        grdObj.RootTable.Columns.Add(wgColLastName);

        WebGridColumn wgColValue = new WebGridColumn();
        wgColValue.Caption = "Value";
        wgColValue.DataMember = "value";
        wgColValue.Name = "value";
        wgColValue.Width = Unit.Pixel(150);
        wgColValue.DataType = "System.Int32";
        grdObj.RootTable.Columns.Add(wgColValue);
    }
}