Updates on StringProperties are not reflected in the tableView if they contain line breaks. For example if a StringProperty contains "ABC" and one updates the property to "ABC\nNewLine" only "ABC" is shown in the column. Similar if a StringProperty contains "ABC" and one updates the property to "ABC123\nNewLine" only "ABC123" is shown. My guess is that the row is never resized appropriately if a StringProperty has text after a new line.

Current workaround is to call (after each update):
tableView.getColumns().get(0).setVisible(false);
tableView.getColumns().get(0).setVisible(true);

I've attached a SSCCE. To reproduce the bug, select a row, add a line break and some text in the textArea and hit "Change comment".

package tableviewnewlinebug;

import javafx.application.Application;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.SelectionMode;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.control.TextArea;
import javafx.scene.control.cell.PropertyValueFactory;
import javafx.scene.layout.Pane;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

/**
 *
 * @author Kacper
 */
public class TableViewNewLineBug extends Application {
    private Comment lastSelectedComment;
    
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        launch(args);
    }
    
    @Override
    public void start(Stage primaryStage) {
        TableView<Comment> tableView = new TableView<>();
        TableColumn<Comment, String> column1 = new TableColumn<>();
        TextArea commentTextArea = new TextArea();
        ObservableList<Comment> comments = FXCollections.observableArrayList();
    
        Button btn = new Button();
        btn.setText("Change comment");
        btn.setOnAction((ActionEvent event) -> {
            if (lastSelectedComment != null) {
                lastSelectedComment.commentProperty().setValue(commentTextArea.getText());
            
                /* workaround
                    tableView.getColumns().get(0).setVisible(false);
                    tableView.getColumns().get(0).setVisible(true);
                */
            }
        });
        
        Pane root = new VBox();
        root.getChildren().addAll(commentTextArea, btn, tableView);
        
        Scene scene = new Scene(root, 800, 600);
        
        primaryStage.setTitle("Hello World!");
        primaryStage.setScene(scene);
        primaryStage.show();
        
        Comment comment1 = new Comment();
        comment1.comment.setValue("ABC");
        
        Comment comment2 = new Comment();
        comment2.comment.setValue("123");
        
        comments.addAll(comment1, comment2);
        tableView.setItems(comments);
        
        tableView.setColumnResizePolicy(TableView.CONSTRAINED_RESIZE_POLICY);
        
        tableView.getColumns().add(column1);
        column1.setCellValueFactory(new PropertyValueFactory<>("comment"));
        
        tableView.getSelectionModel().setSelectionMode(SelectionMode.SINGLE);
        tableView.getSelectionModel().selectedItemProperty().addListener((observableValue, oldValue, newValue) -> {
            if (newValue == null) {
                return;
            }
            
            commentTextArea.setText(newValue.commentProperty().getValue());
            lastSelectedComment = newValue;
        });
    }
    
    public class Comment {
        private StringProperty comment = new SimpleStringProperty();
        
        public StringProperty commentProperty() {
            return this.comment;
        }
    }
}