deque mutated during iteration

[FredHamprecht]

lazyflow: '856baa84ef6704'...

OpTrainRandomForest: (1L, 32L, 32L, 32L, 1L) (1L, 32L, 32L, 32L, 1L)
featMatrix.shape: (1414L, 1L)
labelsMatrix.shape: (1414L, 1L)
Exception in thread Thread-3955:
Traceback (most recent call last):
  File "C:\Python26\lib\threading.py", line 532, in __bootstrap_inner
    self.run()
  File "C:\lazyflow\lazyflow\graph.py", line 2134, in run
    gr.switch( gr)
  File "C:\lazyflow\lazyflow\graph.py", line 307, in _execute
    self.func(self.arg1,self.key, self.destination)
  File "C:\lazyflow\lazyflow\operators\generic.py", line 396, in getOutSlot
    res = self.inputs["Input"][newKey].allocate().wait()
  File "C:\lazyflow\lazyflow\graph.py", line 364, in wait
    self._execute(gr)
  File "C:\lazyflow\lazyflow\graph.py", line 307, in _execute
    self.func(self.arg1,self.key, self.destination)
  File "C:\lazyflow\lazyflow\operators\operators.py", line 46, in getOutSlot
    res = req.wait()
  File "C:\lazyflow\lazyflow\graph.py", line 364, in wait
    self._execute(gr)
  File "C:\lazyflow\lazyflow\graph.py", line 307, in _execute
    self.func(self.arg1,self.key, self.destination)
  File "C:\lazyflow\lazyflow\operators\classifierOperators.py", line 223, in getOutSlot
    RF=self.inputs["Classifier"].value
  File "C:\lazyflow\lazyflow\graph.py", line 556, in value
    temp = self[:].allocate().wait()[0]
  File "C:\lazyflow\lazyflow\graph.py", line 364, in wait
    self._execute(gr)
  File "C:\lazyflow\lazyflow\graph.py", line 307, in _execute
    self.func(self.arg1,self.key, self.destination)
  File "C:\lazyflow\lazyflow\operators\operators.py", line 366, in getOutSlot
    self.graph._notifyMemoryHit()
  File "C:\lazyflow\lazyflow\graph.py", line 2244, in _notifyMemoryHit
    for c in self._registeredCaches:
RuntimeError: deque mutated during iteration