How to reproduce:

1. Click DrugName Filter Icon.
2. Uncheck Combivent
3. OK
4. Click name Filter Icon
5. Uncheck Christoff
6. OK
7. Click DrugName Filter Icon
8. Uncheck Dilantin
9. OK

In this scenario the grid should display only 2 rows but it displays 3.

public partial class RadForm1 : Telerik.WinControls.UI.RadForm
{
    public List<Drug> DrugList { get; set; }

    public RadForm1()
    {
        InitializeComponent();
        DrugList = new List<Drug>();
        LoadDrugList();
        radGridView1.DataSource = DrugList;
        radGridView1.EnableFiltering = true;

        this.radGridView1.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;
        this.radGridView1.MultiSelect = true;
    }

    protected override void OnLoad(EventArgs e)
    {
        base.OnLoad(e);

        radGridView1.MasterTemplate.ShowFilteringRow = false;
        radGridView1.MasterTemplate.ShowHeaderCellButtons = true;
    }

    void LoadDrugList()
    {
        DrugList.Add(new Drug { Dosage = 25, DrugName = "Indocin", Name = "David"});
        DrugList.Add(new Drug { Dosage = 50, DrugName = "Enebrel", Name = "Sam" });
        DrugList.Add(new Drug { Dosage = 10, DrugName = "Hydralazine", Name = "Christoff"});
        DrugList.Add(new Drug { Dosage = 21, DrugName = "Combivent", Name = "Janet"});
        DrugList.Add(new Drug { Dosage = 100, DrugName = "Dilantin", Name = "Melanie"});
    }

}

Workaround: use a custom filter popup
public partial class RadForm1 : Telerik.WinControls.UI.RadForm
{
    public List<Drug> DrugList { get; set; }

    public RadForm1()
    {
        InitializeComponent();
        DrugList = new List<Drug>();
        LoadDrugList();
        radGridView1.DataSource = DrugList;
        radGridView1.EnableFiltering = true;

        this.radGridView1.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;
        this.radGridView1.MultiSelect = true;

        this.radGridView1.FilterPopupRequired += RadGridView1_FilterPopupRequired;
    }

    private void RadGridView1_FilterPopupRequired(object sender, FilterPopupRequiredEventArgs e)
    {
        e.FilterPopup = new CustomRadListFilterPopup(e.Column);
    }

    protected override void OnLoad(EventArgs e)
    {
        base.OnLoad(e);

        radGridView1.MasterTemplate.ShowFilteringRow = false;
        radGridView1.MasterTemplate.ShowHeaderCellButtons = true;
    }

    void LoadDrugList()
    {
        DrugList.Add(new Drug { Dosage = 25, DrugName = "Indocin", Name = "David"});
        DrugList.Add(new Drug { Dosage = 50, DrugName = "Enebrel", Name = "Sam" });
        DrugList.Add(new Drug { Dosage = 10, DrugName = "Hydralazine", Name = "Christoff"});
        DrugList.Add(new Drug { Dosage = 21, DrugName = "Combivent", Name = "Janet"});
        DrugList.Add(new Drug { Dosage = 100, DrugName = "Dilantin", Name = "Melanie"});
    }

}

public class CustomRadListFilterPopup : RadListFilterPopup
{
    public CustomRadListFilterPopup(GridViewDataColumn dataColumn) 
        : base(dataColumn)
    {
    }

    protected override void OnButtonOkClick(EventArgs e)
    {
        FilterMenuTreeItem treeMenuItem = this.Items.FirstOrDefault(i => i is FilterMenuTreeItem) as FilterMenuTreeItem;
        if (treeMenuItem == null)
        {
            base.OnButtonOkClick(e);
        }

        FilterMenuTreeElement listFilterElement = treeMenuItem.TreeElement;

        FilterOperator filterOperator = FilterOperator.IsEqualTo;

        switch (listFilterElement.SelectedMode)
        {
            case ListFilterSelectedMode.All:
                filterOperator = FilterOperator.None;
                break;
            case ListFilterSelectedMode.Null:
                filterOperator = FilterOperator.IsNull;
                break;
            case ListFilterSelectedMode.NotNull:
                filterOperator = FilterOperator.IsNotNull;
                break;
        }

        if (filterOperator != FilterOperator.IsEqualTo)
        {
            SetFilterOperator(filterOperator);
            this.ClosePopup(RadPopupCloseReason.CloseCalled);
        }
        else
        {
            CompositeFilterDescriptor compositeFilterDescriptor = new CompositeFilterDescriptor();
            compositeFilterDescriptor.PropertyName = this.DataColumn.Name;
            RadListFilterDistinctValuesTable distinctValues = this.GetDistinctValuesTable();
            string blanksKey = RadGridLocalizationProvider.CurrentProvider.GetLocalizedString(RadGridStringId.FilterMenuBlanks);
            bool blanks = listFilterElement.SelectedValues.Contains(blanksKey);
            compositeFilterDescriptor.LogicalOperator = FilterLogicalOperator.And;

            foreach (DictionaryEntry entry in distinctValues)
            {
                object key = entry.Key;

                if (string.IsNullOrEmpty(Convert.ToString(key)))
                {
                    key = blanksKey;
                }

                if (this.DataColumn is GridViewDateTimeColumn || this.DataColumn.DataType == typeof(DateTime) || this.DataColumn.DataType == typeof(DateTime?))
                {
                    DateTime dateTime;

                    if (DateTime.TryParse(key.ToString(), out dateTime))
                    {
                        object dataKey;
                        if (RadDataConverter.Instance.TryFormat(treeMenuItem.TreeElement.GroupedDateValues ? dateTime.Date : dateTime, typeof(string), this.DataColumn, out dataKey) == null)
                        {
                            key = dataKey;
                        }
                    }
                }

                if (!listFilterElement.SelectedValues.Contains(key))
                {
                    foreach (object value in (ArrayList)entry.Value)
                    {
                        FilterDescriptor descriptor;
                        if (value == DBNull.Value)
                        {
                            descriptor = new FilterDescriptor(this.DataColumn.Name, FilterOperator.IsNotEqualTo, null);
                        }
                        else if (this.DataColumn is GridViewDateTimeColumn || this.DataColumn.DataType == typeof(DateTime) || this.DataColumn.DataType == typeof(DateTime?))
                        {
                            descriptor = new DateFilterDescriptor(this.DataColumn.Name, FilterOperator.IsNotEqualTo, (DateTime?)value, false);
                        }
                        else
                        {
                            descriptor = new FilterDescriptor(this.DataColumn.Name, FilterOperator.IsNotEqualTo, value);
                        }

                        compositeFilterDescriptor.FilterDescriptors.Add(descriptor);
                    }
                }
            }

            if (this.DataColumn.FilterDescriptor != null)
            {
                CompositeFilterDescriptor compositeFilter = this.DataColumn.FilterDescriptor as CompositeFilterDescriptor;
                if (compositeFilter != null)
                {
                    foreach (var item in compositeFilter.FilterDescriptors)
                    {
                        if (listFilterElement.SelectedValues.Contains(item.Value))
                        {
                            continue;
                        }

                        FilterDescriptor descriptor = new FilterDescriptor(this.DataColumn.Name, FilterOperator.IsNotEqualTo, item.Value);
                        compositeFilterDescriptor.FilterDescriptors.Add(descriptor);
                    }
                }
                else if(!listFilterElement.SelectedValues.Contains(this.DataColumn.FilterDescriptor.Value))
                {
                    FilterDescriptor descriptor = new FilterDescriptor(this.DataColumn.Name, FilterOperator.IsNotEqualTo, this.DataColumn.FilterDescriptor.Value);
                    compositeFilterDescriptor.FilterDescriptors.Add(descriptor);
                }
            }
            this.FilterDescriptor = compositeFilterDescriptor;

            OnFilterConfirmed();
        }
    }
}