Android-WebView's onReceivedHttpAuthRequest() not called again

I am using a webview based application where i am rendering a url in the webview. The Url has a HTTP auth .

When i launch the url very first time,its onReceivedHttpAuthRequest() is called and I display a dialog for user to enter the authentication credentials that is auth username and password.

@Override
public void onReceivedHttpAuthRequest(WebView view, HttpAuthHandler handler, String host, String realm) {
        final WebView mView = view;
        final HttpAuthHandler mHandler = handler;

        final EditText usernameInput = new EditText(mActivity);
        usernameInput.setHint("Username");

        final EditText passwordInput = new EditText(mActivity);
        passwordInput.setHint("Password");
        passwordInput.setInputType(InputType.TYPE_CLASS_TEXT | InputType.TYPE_TEXT_VARIATION_PASSWORD);

        LinearLayout ll = new LinearLayout(mActivity);
        ll.setOrientation(LinearLayout.VERTICAL);
        ll.addView(usernameInput);
        ll.addView(passwordInput);

        Builder authDialog = new AlertDialog
                .Builder(mActivity)
                .setTitle("Authentication")
                .setView(ll)
                .setCancelable(false)
                .setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int whichButton) {
                        mHandler.proceed(usernameInput.getText().toString(), passwordInput.getText().toString());
                        dialog.dismiss();
                    }
                })
                .setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int whichButton) {
                        dialog.dismiss();
                        mView.stopLoading();
                        onLoadListener.onAuthCancel((MyWebView)mView, mTitleTextView);
                    }
                });

        if(view!=null)
            authDialog.show();

    }

On Submitting the request proceed well and the url is loaded. But After I exit the app using back button(not sending in background), if i launch it again and tru to load the same url it directly load the url without asking for credentials that is onReceivedHttpAuthRequest() is never called again.

I am also clearing the credentials on app exit using following code:

WebViewDatabase webDB = WebViewDatabase.getInstance(BrowserActivity.this);
    if(webDB!=null){
        if(webDB.hasFormData())
            webDB.clearFormData();
        if(webDB.hasUsernamePassword())
            webDB.clearUsernamePassword();
        if(webDB.hasHttpAuthUsernamePassword())
            webDB.clearHttpAuthUsernamePassword();
    }
webView.clearCache(true);

Also i am clearing all the webview cache, cookies, and application's cache directory and the webview databases:

BrowserActivity.this.deleteDatabase("webview.db");
BrowserActivity.this.deleteDatabase("webviewCache.db");

I don't know why this is happening. Is there anybody who can help me on this. At least on the issue that why onReceivedHttpAuthRequest() is not called?