1). Enter some text. Press CTRL-Z. All entered text will be removed instead of the last symbol.
2). Enter some text and press CTRL-DELETE several times. Press CTRL-Z several times. Text will not be restored correctly.
3). Undo operation unexpectedly reverts the caret position.

Sample to check:
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.TextArea;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class App extends Application {

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

    @Override
    public void start(Stage stage) throws Exception {
        TextArea control = new TextArea("1 2 3 4 5 6 7 8 9 10");
        Scene scene = new Scene(new VBox(control), 500, 500);
        stage.setScene(scene);
        stage.show();
    }
}