To reproduce, run the example below,

- start editing such that the popup is open (notice that the current cell value is selected)
- type some char
- press enter
- expected: the edited value is committed (that is same in first column)
- actual: the edit is canceled (that is value unchanged)

Additional observation:
- start editing such that the popup is not open
- type some char and press enter (not committing at this point is yet another misbehavior;)
- open popup: notice that nothing is selected
- press enter
- expected and actual: edited value is committed

Worked as expected in both scenarios in release 8u60, could be introduced by https://bugs.openjdk.java.net/browse/JDK-8138683 - using the showing property of the popup is not a good trigger for committing ..

The example, slightly changed version of the older issue, to allow editable combo cells

import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.scene.Node;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.control.cell.ComboBoxTableCell;
import javafx.scene.control.cell.PropertyValueFactory;
import javafx.scene.control.cell.TextFieldTableCell;
import javafx.scene.layout.BorderPane;
import javafx.scene.shape.Arc;
import javafx.scene.shape.Line;
import javafx.scene.shape.Rectangle;
import javafx.scene.shape.Shape;
import javafx.stage.Stage;

import java.util.List;
import java.util.logging.Logger;
import java.util.stream.Collectors;

public class ComboCellIssuesContinued extends Application {
  
    private Parent getContent() {
        
        ObservableList<Shape> items = FXCollections.observableArrayList(
               new Line(), new Rectangle(), new Arc());
   
        items.forEach(p -> p.setId(p.getClass().getSimpleName()));
        List<String> names = items.stream().map(Node::getId).collect(Collectors.toList());
        TableView<Shape> table = new TableView<>(items);
        table.setEditable(true);
        TableColumn<Shape, String> plain = new TableColumn<>("Plain");
        plain.setCellValueFactory(new PropertyValueFactory("id"));
        plain.setCellFactory(TextFieldTableCell.forTableColumn());
        table.getColumns().addAll(plain);
        
        TableColumn<Shape, String> combo = new TableColumn<>("Combo");
        combo.setCellValueFactory(new PropertyValueFactory("id"));
        combo.setCellFactory(p -> {
            ComboBoxTableCell tc = new ComboBoxTableCell(names.toArray()); //"someId", "other", "orNothing");
            tc.setComboBoxEditable(true);
            return tc;
        });
        table.getColumns().addAll(combo);
      
        Parent content = new BorderPane(table);
        return content;
    }

    @Override
    public void start(Stage primaryStage) throws Exception {
        primaryStage.setScene(new Scene(getContent()));
        primaryStage.setTitle(FXUtils.version());
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
    
    @SuppressWarnings("unused")
    private static final Logger LOG = Logger
            .getLogger(ComboCellIssuesContinued.class.getName());
}