There are several places in the ast module where the use of zip is allowing malformed nodes to have unpaired children silently thrown away. A couple of short examples:

>>> from ast import Constant, Dict, literal_eval, unparse
>>> nasty_dict = Dict(keys=[Constant("I don't have a value!")], values=[])
>>> unparse(nasty_dict)
'{}'
>>> literal_eval(nasty_dict)
{}

I'm currently working on a patch to raise errors instead.