FULL PRODUCT VERSION :
java version "1.8.0_72-ea"
Java(TM) SE Runtime Environment (build 1.8.0_72-ea-b05)
Java HotSpot(TM) 64-Bit Server VM (build 25.72-b05)


ADDITIONAL OS VERSION INFORMATION :
ver 6.1 - Windows 7 Professional, Version 6.1 (Build 7601, Service Pack 1)

A DESCRIPTION OF THE PROBLEM :
Multiple Tabs are opened in a TabPane. Each Tab contains a WebView. When the Tabs are closed WebView does not (never) release resources.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the example code below or the java file I have sent. The example display 4 Tabs, the first 3 tabs display web pages, the 4th Tab is empty. Wait for the display to complete, then check the memory use:
 - 500-600Mb in Windows Task Manager (400Mb in JDK9)
 - heap size 350Mb in NetBeans profiler
Now close the first 3 Tabs, leaving one empty Tab and the resources are never released, both memory use and heap size remain constant.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Memory use and heap size should reduce as the Tabs are closed.

REPRODUCIBILITY :
This bug can be reproduced always.

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I have also sent a java file with this code:
package webviewmemory;
import javafx.application.Application;
import javafx.concurrent.Worker;
import javafx.event.Event;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Tab;
import javafx.scene.control.TabPane;
import javafx.scene.web.WebEngine;
import javafx.scene.web.WebView;
import javafx.stage.Stage;

public class WebViewMemory extends Application {
    
    @Override
    public void start(Stage primaryStage) {
        TabPane tabPane= new TabPane();
        TabPage tab1= new TabPage("http:\\www.yahoo.com");
        TabPage tab2= new TabPage("http:\\www.marketwatch.com");
        TabPage tab3= new TabPage("http:\\www.bbc.com");
        TabPage tab4= new TabPage(null);
        tabPane.getTabs().addAll(tab1,tab2,tab3,tab4);
        
        Scene scene = new Scene(tabPane, 1024, 800);
        primaryStage.setTitle("WebView Memory Problem");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

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

class TabPage extends Tab {
    TabPage thisTab;
    WebEngine thisEngine;
    
    TabPage(String urlString) {
        thisTab= this;
        if(urlString==null) {
            this.setText("new");
            this.setClosable(false);
        }
        else {
            this.setText(urlString);
            WebView browser = new WebView();
            browser.getEngine().load(urlString);
            thisEngine= browser.getEngine();
            this.setContent(browser);
            this.setOnClosed(new EventHandler<Event>() {
                @Override
                public void handle(Event event) {
                    thisTab.setContent(null);
                    thisTab= null;
                    thisEngine.setJavaScriptEnabled(false);
                    Worker worker= thisEngine.getLoadWorker();
                    if(worker.isRunning()) worker.cancel();
                    thisEngine.loadContent(null);
                    thisEngine= null;
                }
            });
        }
    }
}

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