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Bug should be marked INVALID.

childNodes lists are 'live'. You are iterating over a list
you are destroying at the same time. The code is equivalent
to the more obviously broken:

  foo= [1, 2, 3, 4]
  i= 0
  while i<len(foo):
    del foo[i]
    i+= 1
  foo
  >>> [2, 4]

The 'working' example only works because it has extra
whitespace nodes in, so when you delete child number i, the
child i+1 that is skipped over is a Text node containing
only whitespace.

BTW, there's a separate bug tracker for the PyXML project
from which minidom is taken. You may get better results by
submitting there (and discussing on the XML-SIG list).