Android : Android memory leak in android.os.PowerManager

I have identified memory leak, with following report from Eclipse Memory Analyzer

mBuffer android.graphics.Bitmap @ 0x42624100                                                                  
'- mDrawBitmap com.bilickib.android.charts.PieChartView @ 0x425e4d58                              
   '- pieChartView mine.PieChartFragment @ 0x424dbca8                      
      '- mCurrentPrimaryItem com.bilickib.android.charts.PieChartFragmentPagerAdapter @ 0x424dbb18
         '- pieChartFragmentPagerAdapter com.bilickib.android.charts.PieChartHolder @ 0x427654c0  
            '- pieChartHolder com.bilickib.android.charts.Activity @ 0x424df648  
               '- mContext android.os.PowerManager @ 0x4252f0c8                                               
                  '- mPowerManager android.view.ViewRootImpl @ 0x425857f0                                     
                     '- this$0 android.view.ViewRootImpl$WindowInputEventReceiver @ 0x425832d8                
                        '- referent java.lang.ref.FinalizerReference @ 0x4256bfa8                             

I do not use PowerManager in my code at all. How could it hold reference to my class? PieChartView has big bitmap and causes memory leak for me.