PBO / GL_PIXEL_UNPACK_BUFFER causes Memory Leak in iOS 9 ?

After seeing one of our projects' memory usage continously increasing from ~90MB up to 300MB in a couple of minutes ( 100-300KB/s ) I've run down to the cause of it. I don't know if this is an iOS 9 issue or not since we recently upgraded to iOS 9 on an iPad Air 2, but I've narrowed it down to using Pixel Buffer Objects for texture uploads.

So, every frame I do this :

  static bool VersionCheck = false;
  static bool UsePBOs = false;/
  if (!VersionCheck)
  {
       VersionCheck = true;
       const char *Version = (const char*)glGetString( GL_VERSION );
       float fVer = 2.0f;
       if (Version && sscanf( Version, "OpenGL ES %f", &fVer ))
       {
            if ( fVer >= 3.0f )
            UsePBOs = true;
       }
  }
  /
  if ( UsePBOs )
  {
       int TotalData = Width * Height *4;
       static unsigned int PBO = 0;
       if ( PBO == 0)
       {
            glGenBuffers( 1, &PBO );
            CheckGLError();
     
            glBindBuffer( GL_PIXEL_UNPACK_BUFFER, PBO );
            CheckGLError();
            glBufferData( GL_PIXEL_UNPACK_BUFFER, TotalData, NULL, GL_STREAM_COPY);
            CheckGLError();
       }

       glBindBuffer( GL_PIXEL_UNPACK_BUFFER, PBO );
       CheckGLError();
       GLubyte* ptr = (GLubyte*)glMapBufferRange(GL_PIXEL_UNPACK_BUFFER, 0, TotalData, GL_MAP_WRITE_BIT | GL_MAP_UNSYNCHRONIZED_BIT );
       CheckGLError();

  if ( ptr )
  {
       pthread_mutex_lock( &CameraPixelsMutex );

       if ( Data )
            memcpy( ptr, Data, TotalData );

       pthread_mutex_unlock( &CameraPixelsMutex );
       GLboolean ret = glUnmapBuffer( GL_PIXEL_UNPACK_BUFFER );
       CheckGLError();
       if ( ret != 1 )
       {
       NSLog(@"glUnmapBuffer( GL_PIXEL_UNPACK_BUFFER ) returned %d", ret );
       }
  }
  else
       NSLog(@"glMapBufferRange returned nullptr %p", ptr );

       glBindTexture( GL_TEXTURE_2D, TextureID );
       glTexSubImage2D( GL_TEXTURE_2D, /
       0, /
       0,
       0, /
       Width, /
       Height, /
       GL_BGRA, /
       GL_UNSIGNED_BYTE, /
       0 
       );
       CheckGLError();

       glBindBuffer( GL_PIXEL_UNPACK_BUFFER, 0 );
       CheckGLError();
  }
  else  
  {
       pthread_mutex_lock( &CameraPixelsMutex );

       glBindTexture( GL_TEXTURE_2D, TextureID );
       CheckGLError();
       if ( Data )
       {
            glTexSubImage2D( GL_TEXTURE_2D, 
            0, 
            0, 
            0,
            Width, 
            Height, 
            GL_BGRA, 
            GL_UNSIGNED_BYTE, 
            Data 
       );
  }
  CheckGLError();

  pthread_mutex_unlock( &CameraPixelsMutex );
  }

The thing, the GLES3/PBO branch is causing this 100K/s leak while if I only use the GLES2 route (where perf goes down by 50%) the memory usage stays constant ( i waited around 5 minutes and it doesn't go up at all ).

This feels like a bug in the GL driver or something may be wrong with me code, please advise.