FULL PRODUCT VERSION :
D:\Java\jdk1.8.0_161\bin>java -version
java version "1.8.0_161"
Java(TM) SE Runtime Environment (build 1.8.0_161-b12)
Java HotSpot(TM) Client VM (build 25.161-b12, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Windows 7 64 bit.

A DESCRIPTION OF THE PROBLEM :
Please test to use the flowing code:
/*********************************************************/
package com.test.ime;

import java.awt.Container;

import javax.swing.JFrame;
import javax.swing.JTextArea;
import javax.swing.WindowConstants;

public class ImeExample extends JFrame {
	/**
	 * Launch the application.
	 */
	public static void main(String[] args) {
		new ImeExample().createFrame();
	}

	/**
	 * Create the frame.
	 */
	public void createFrame() {
		JFrame frame =new JFrame("just for tesing ...");
		Container container = frame.getContentPane();
		JTextArea txtrTest = new JTextArea();
		txtrTest.setText("test");
		container.add(txtrTest);
		frame.setVisible(true);
		frame.setSize(400, 300);
		frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
	}
}
 /*********************************************************/



REGRESSION.  Last worked in version 8u152

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Run this example in jdk 1.8_161 version, you will see the a java window which is included a text area component.
2.Switch the input method to the Japannese IME,and select the input mode to "Hiragana".
3.Come back to the text area, press the 'a' key, the '���' will be shown in the text area.
4.Open the task manager, check the CPU loading, in my computer, the cpu load will keep to 13%.
5.Run the same code in the jdk 1.8_152,  run step 2,3,4, check the cpu loading, in my computer, the cpu load keep to 0%. 

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Hope the cpu load keep 0%.
ACTUAL -
the cpu load keep to 13%.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
/*********************************************************/
package com.test.ime;

import java.awt.Container;

import javax.swing.JFrame;
import javax.swing.JTextArea;
import javax.swing.WindowConstants;

public class ImeExample extends JFrame {
	/**
	 * Launch the application.
	 */
	public static void main(String[] args) {
		new ImeExample().createFrame();
	}

	/**
	 * Create the frame.
	 */
	public void createFrame() {
		JFrame frame =new JFrame("just for tesing ...");
		Container container = frame.getContentPane();
		JTextArea txtrTest = new JTextArea();
		txtrTest.setText("test");
		container.add(txtrTest);
		frame.setVisible(true);
		frame.setSize(400, 300);
		frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
	}
}
---------- END SOURCE ----------