LINQ2SQL DataContext BindingSource question

Question

Hi. I am almost a total novice to Linq2Sql notions except for few How Do I series videos :)

I have some classes in my DataContext.

GartPTSDataContext GetDataContext() {
    SqlConnectionStringBuilder sb =
            new SqlConnectionStringBuilder(Settings.Default.DBConnection);
    sb.Password = "sql";
    GartPTSDataContext dtx = new GartPTSDataContext(sb.ToString());
    return dtx;
}

Then in one function I do

GartPTSDataContext dtx = GetDataContext();
var ptnList = from p in dtx.G12_PTSLists select p;
bsFullPTNList.DataSource = ptnList;

and in bindingsource_CurrentChanged (for bsFullPTNList) I do

if (CurrentPTS==null)
    return; //bsFullPTNList.Current
GartPTSDataContext dtx = GetDataContext();

//Fill neighbour's grid
var neigbQry= from ptns in dtx.G12_PTSLists
        join ng in dtx.G12_PTS_Neighbours
        on ptns.UnitID equals ng.PTN_ID
        where ptns.UnitID==CurrentPTS.UnitID
        select ptns;
bsNeighbours.DataSource = neigbQry;

//fill full PTN list except for current PTN and existing neighbours
bsAllowedPTNList.DataSource = from p in dtx.G12_PTSLists
        where !neigbQry.Contains(p)
        select p;

As a result I get that DataGrids bound to bsFullPTNList and bsAllowedPTNList respectively become synchronized whereas I need them to be independent. What am I missing here?