title: Netlogo turtle skips specific patch
body: <p>I am trying to instruct turtles to visit all green patches.</p>
  
  <p>There is a behavior which I can't get my head around: patch 0,0 is always avoided if the location of origin = center (see screenshot with 0,0 colored blue), and the lower left corner if location of origin = corner.</p>
  
  <p><a href="https://i.stack.imgur.com/UpHjb.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/UpHjb.png" alt="enter image description here"></a></p>
  
  <p>Why is this? What error am I making here?</p>
  
  <pre><code>;;==========================================================
  globals [
    memory
    target
  ]
  patches-own [visit-counter]
  
  ;;==========================================================
  to setup
    ca
    resize-world -6 6 -6 6
    set-patch-size 40
    create-turtles 1 [
      set memory (list patch-here)
      setxy random-pxcor random-pycor
      set size 1
      set color blue
    ]
  
    ask patches [if random 100 &lt; 40 [set pcolor green]]
    ask patch 0 0 [set pcolor green]
  
    ask patches [set visit-counter 0]  
    reset-ticks
  end
  
  ;;==============================================
  
  to go
  
    ask turtles [choose-target]
    tick
    if ticks &gt; 500 [stop]
  end
  
  ;;==============================================
  to choose-target
    pd
  
    ;; set of unvisited patches
    let unvisited patches with [not member? self [memory] of myself]
  
    ;; set of green patches that are not visited
    let targets patches with [(member? self unvisited) and (pcolor = green)]
  
    ;; select target and move there
    set target one-of targets with-min [distance myself]
  
    ifelse target != nobody [
      face target
      fd 1
      set visit-counter (visit-counter + 1)
      set memory lput patch-here memory
    ]
    [die
    ]
  end
  </code></pre>