RuntimeError in cache operator

[stuarteberg]

A user reports this error:

ERROR 2015-09-03 18:41:28,818 log_exception 2893 139975995680512 Traceback (most recent call last):
  File "/media/feynman/3TBBackup/ilastik-1.1.6-Linux/ilastik-meta/lazyflow/lazyflow/operators/cacheMemoryManager.py", line 201, in _cleanup
    for k, t in c.getBlockAccessTimes():
  File "/media/feynman/3TBBackup/ilastik-1.1.6-Linux/ilastik-meta/lazyflow/lazyflow/operators/opRefactoredBlockedArrayCache.py", line 98, in getBlockAccessTimes
    return self._opUnblockedArrayCache.getBlockAccessTimes()
  File "/media/feynman/3TBBackup/ilastik-1.1.6-Linux/ilastik-meta/lazyflow/lazyflow/operators/opUnblockedArrayCache.py", line 166, in getBlockAccessTimes
    for k in self._last_access_times]
RuntimeError: dictionary changed size during iteration