title: Pygame's mouse.get_rel() returns values when mouse isn't moving
body: <p>In my program pygame.mouse.get_rel() as well as event.rel return tuples such as (0, -1) or any other of (1,0), (0,1), (1,1) etc. even when mouse is not moving.
  When i move the mouse i get correct values, but when i stop it again returns one of these tuples (returns one of them until i move the mouse and when i stop moving, it starts to return other tuple randomly and repeats until next mouse move).
  It makes my game unable to play.
  Here is the important part of the code:</p>
  
  <pre><code>import pygame
  pygame.init()
  game_display = pygame.display.set_mode((800,600))
  pygame.mouse.set_visible(False)
  pygame.event.set_grab(True)
  
  game_exit = False
  
  while not game_exit:
      mouse_move = (0,0)
      for event in pygame.event.get():
          if event.type == pygame.QUIT:
              game_exit = True
          if event.type == pygame.MOUSEMOTION:
              print(event.rel) #returns (0, -1)
      if pygame.key.get_pressed()[pygame.K_ESCAPE]:
          game_exit = True
  
      print(pygame.mouse.get_rel()) #returns (0, -1)
  
  pygame.quit()
  </code></pre>
  
  <p>EDIT: I noticed that removing either</p>
  
  <pre><code>pygame.mouse.set_visible(False)
  </code></pre>
  
  <p>or</p>
  
  <pre><code>pygame.event.set_grab(True)
  </code></pre>
  
  <p>solves the problem, but both methods are needed.</p>