'maximum recursion depth exceeded while calling a Python object' while Parser constructor call with rule defined via 'forward'

[slonoten]

All examples which use 'forward' rule from 'getting started' page https://nbviewer.jupyter.org/github/natasha/yargy/blob/master/docs/index.ipynb crashed with maximum recursion depth error exceeded.

EXPR = forward()
EXPR.define(or_(
    rule('a'),
    rule('(', EXPR, '+', EXPR, ')')
).named('EXPR'))
EXPR.normalized.as_bnf
Parser(EXPR)

---------------------------------------------------------------------------
RecursionError                            Traceback (most recent call last)
<ipython-input-5-24cb41b0dd36> in <module>
----> 1 Parser(rule(EXPR))

~/miniconda3/envs/tmp/lib/python3.7/site-packages/yargy/parser.py in __init__(self, rule, tokenizer, tagger)
    252         context = Context(tokenizer, tagger)
    253         rule = rule.activate(context)
--> 254         rule = rule.normalized
    255         self.rule = rule.as_bnf.start
    256 

~/miniconda3/envs/tmp/lib/python3.7/site-packages/yargy/rule/constructors.py in normalized(self)
    114             ReplaceOrTransformator,
    115             ReplaceEmptyTransformator,
--> 116             FlattenTransformator,
    117         )
    118 

~/miniconda3/envs/tmp/lib/python3.7/site-packages/yargy/rule/constructors.py in transform(self, *transformators)
     94 
     95     def transform(self, *transformators):
---> 96         return TransformatorsComposition(transformators)(self)
     97 
     98     def activate(self, context):

~/miniconda3/envs/tmp/lib/python3.7/site-packages/yargy/visitor.py in __call__(self, item)
     26     def __call__(self, item):
     27         for transformator in self.transformators:
---> 28             item = transformator()(item)
     29         return item

~/miniconda3/envs/tmp/lib/python3.7/site-packages/yargy/rule/transformators.py in __call__(self, root)
     63         for item in root.walk(types=ForwardRule):
     64             if item.rule:
---> 65                 item.define(self.visit(item.rule))
     66         return self.visit(root)
     67 

~/miniconda3/envs/tmp/lib/python3.7/site-packages/yargy/rule/transformators.py in visit(self, item)
     71             return self.visited[item_id]
     72         else:
---> 73             item = self.resolve_method(item)(item)
     74             self.visited[item_id] = item
     75             return item

~/miniconda3/envs/tmp/lib/python3.7/site-packages/yargy/rule/transformators.py in visit_Rule(self, item)
     94 
     95     def visit_Rule(self, item):
---> 96         return Rule([self.visit(_) for _ in item.productions])
     97 
     98     def visit_OrRule(self, item):

~/miniconda3/envs/tmp/lib/python3.7/site-packages/yargy/rule/transformators.py in <listcomp>(.0)
     94 
     95     def visit_Rule(self, item):
---> 96         return Rule([self.visit(_) for _ in item.productions])
     97 
     98     def visit_OrRule(self, item):

~/miniconda3/envs/tmp/lib/python3.7/site-packages/yargy/rule/transformators.py in visit(self, item)
     71             return self.visited[item_id]
     72         else:
---> 73             item = self.resolve_method(item)(item)
     74             self.visited[item_id] = item
     75             return item

~/miniconda3/envs/tmp/lib/python3.7/site-packages/yargy/rule/transformators.py in visit_Production(self, item)
     83     def visit_Production(self, item):
     84         return Production(
---> 85             [self.visit_term(_) for _ in item.terms],
     86             item.main
     87         )

~/miniconda3/envs/tmp/lib/python3.7/site-packages/yargy/rule/transformators.py in <listcomp>(.0)
     83     def visit_Production(self, item):
     84         return Production(
---> 85             [self.visit_term(_) for _ in item.terms],
     86             item.main
     87         )

~/miniconda3/envs/tmp/lib/python3.7/site-packages/yargy/rule/transformators.py in visit_term(self, item)
     77     def visit_term(self, item):
     78         if is_rule(item):
---> 79             return self.visit(item)
     80         else:
     81             return item

... last 7 frames repeated, from the frame below ...

~/miniconda3/envs/tmp/lib/python3.7/site-packages/yargy/rule/transformators.py in visit(self, item)
     71             return self.visited[item_id]
     72         else:
---> 73             item = self.resolve_method(item)(item)
     74             self.visited[item_id] = item
     75             return item

RecursionError: maximum recursion depth exceeded

I have checked all examples with python 3.7.7 and 3.8.2 and yargy 0.14.0

If I replace 'forward' with appropriate 'repeat' construction all work fine even if BNF representation is identical