Please refer to the attached gif file. You will notice that for the GridViewMaskBoxColumn  with numeric mask the filtering doesn't work. For the other columns each key stroke filters the grid rows.

Workaround: either use a GridViewDecimalColumn or change the default editor for the GridViewMaskBoxColumn :

            this.radGridView1.EditorRequired += radGridView1_EditorRequired; 

        private void radGridView1_EditorRequired(object sender, EditorRequiredEventArgs e)
        {
            if (this.radGridView1.CurrentColumn.HeaderText == "MaskBoxColumn")
            {
                GridSpinEditor spinEditor = new GridSpinEditor();
                RadSpinEditorElement element = spinEditor.EditorElement as RadSpinEditorElement;
                element.ShowUpDownButtons = false;
                e.Editor = spinEditor;
            }
        }