This bug manifests itself in a couple of "fun" ways:

len(list(client.query(kind="Foo").fetch(limit=300)))

Will yield 300, assuming there are 300 or more entities of that kind.

len(list(client.query(kind="Foo").fetch(limit=500)))

Assuming there are 500 entities of that kind, will yield 500. If there are n entities where n > 500, it will yield n.

This all seems to be caused by the v1beta3 api truncating the limits to 300:

entities, more, cursor = client.query(kind="Foo").fetch(limit=500).next_page()

len(entities) will be 300 and not 500 even if there are 500 or more entities of that kind.

We're currently using the following snippet to work around this issue:

def _all_entities(iterator):
    entities, cursor = [], None
    while iterator._limit > 0:
        xs, more, cursor = iterator.next_page()
        iterator._limit -= len(xs)
        entities.extend(xs)
        if not more:
            break

    return entities, cursor