Mouse callback: Selecting pixel with mouse (Bug #3409)

I'm using the [cv2.setMouseCallback][1] function to select a pixel of an image shown in a window.
The callback function returns an x and y integers that represent the position of the pixel in the image, but paying attention to it's behaviour it seems to me that doesn't return the pixel you are over but the rounded value of a point in an imaginary axis.

If you look at the two first images, in both the mouse is over the pixel 0,0 but the result is diferent if you move closer to other pixels.

Ok. I know in a real image the error is insignificant, but is this a bug?

cv2.namedWindow('image',cv2.WINDOW_NORMAL) # Can be resized
       cv2.resizeWindow('image', self.w, self.h) #Reasonable size window
       cv2.setMouseCallback('image',self.mouse_callback) #Mouse callback
       while(not self.finished):
          cv2.imshow('image',self.img)
          k = cv2.waitKey(4) & 0xFF
          if k  27:
             breakim
       cv2.destroyAllWindows()

# mouse callback function
       def mouse_callback(self,event,x,y,flags,param):
          if event  cv2.EVENT_LBUTTONDOWN:
             print x, y

[1]: http://docs.opencv.org/modules/highgui/doc/user_interface.html?highlight=mouse#cv.SetMouseCallback