When a TextFieldTableCell is edited and then committed via ENTER, the focusWithin adjustment will eventually become negative, meaning the TableView will never be focusWithin = true again.

This is probably because the graphic is set on startEdit() (via setGraphic(..)) and then cleared after the commit is done via commitEdit().
The TableView seems to calculate the focusWithin counter wrong here. The value will become smaller after every commit.

*****************************************
EXAMPLE

import javafx.application.Application;
import javafx.beans.property.SimpleBooleanProperty;
import javafx.beans.property.SimpleStringProperty;
import javafx.collections.FXCollections;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.control.cell.CheckBoxTableCell;
import javafx.scene.control.cell.TextFieldTableCell;
import javafx.scene.layout.Background;
import javafx.scene.layout.BorderPane;
import javafx.scene.paint.Color;
import javafx.stage.Stage;

public class TableViewFocusWithin extends Application {

    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) {
        TableView<String> tableView = new TableView<>();
        tableView.setFixedCellSize(24);
        tableView.setPadding(new Insets(5));

        tableView.setEditable(true);
        tableView.setItems(FXCollections.observableArrayList("a", "b", "c", "d", "e", "f", "g", "h", "i"));
        tableView.focusWithinProperty().addListener(inv -> {
            if (tableView.isFocusWithin()) {
                tableView.setBackground(Background.fill(Color.GREEN));
            } else {
                tableView.setBackground(Background.fill(Color.RED));
            }
        });

        TableColumn<String, String> col1 = new TableColumn<>("checkbox");
        col1.setCellValueFactory(cellData -> new SimpleStringProperty(cellData.getValue()));
        col1.setCellFactory(CheckBoxTableCell.forTableColumn(idx -> new SimpleBooleanProperty(false)));

        TableColumn<String, String> col2 = new TableColumn<>("text");
        col2.setCellValueFactory(cellData -> new SimpleStringProperty(cellData.getValue()));

        TableColumn<String, String> col3 = new TableColumn<>("text2");
        col3.setCellValueFactory(cellData -> new SimpleStringProperty(cellData.getValue()));

        TableColumn<String, String> col4 = new TableColumn<>("text3");
        col4.setCellValueFactory(cellData -> new SimpleStringProperty(cellData.getValue()));
        col4.setCellFactory(TextFieldTableCell.forTableColumn());

        tableView.getColumns().addAll(col1, col2, col3, col4);

        BorderPane pane = new BorderPane(tableView);

        Button focusLost = new Button("focus lost");
        BorderPane.setMargin(focusLost, new Insets(5, 0, 0, 0));

        pane.setBottom(focusLost);

        Scene scene = new Scene(pane);
        primaryStage.setScene(scene);
        primaryStage.show();
    }
}

*****
Note: The TableView background border will be green when focusWithin = true and red when not. After some commits (~2-3) the border will stay red forever.