To reproduce:

When app is opened and text field get focus - all the text is selected.
1. Click with mouse after the last character.
2. Type any letter.
3. The letter appears before the last character!


import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.TextField;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;

public class TextFieldCaretPos extends Application {

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

    @Override
   public void start(Stage stage) throws Exception {
        HBox root = new HBox();
        
        TextField textField = new TextField("Simple tet");
        root.getChildren().add(textField);
        
        Scene scene = new Scene(root, 300, 200);
        stage.setScene(scene);;
        stage.show();
    }
}