inconsistent parsing for time with numbers

this one is just wrong

$ curl -s -XPOST http://0.0.0.0:8000/parse --data "text=the second sunday of October last year" | jq .
[
  {
    "dim": "time",
    "body": "the second sunday of October last year",
    "value": "{\"values\":[],\"value\":\"2016-10-02T00:00:00.000-07:00\",\"grain\":\"day\",\"type\":\"value\"}",
    "start": 0,
    "end": 38
  }
]

this one gets both parts right, but why did just changing the one word change so much of the parsing?

$ curl -s -XPOST http://0.0.0.0:8000/parse --data "text=the second thursday of October last year" | jq .
[
  {
    "dim": "time",
    "body": "the second thursday of October",
    "value": "{\"values\":[{\"value\":\"2017-10-12T00:00:00.000-07:00\",\"grain\":\"day\",\"type\":\"value\"}],\"value\":\"2017-10-12T00:00:00.000-07:00\",\"grain\":\"day\",\"type\":\"value\"}",
    "start": 0,
    "end": 30
  },
  {
    "dim": "time",
    "body": "thursday of October last year",
    "value": "{\"values\":[],\"value\":\"2016-10-06T00:00:00.000-07:00\",\"grain\":\"day\",\"type\":\"value\"}",
    "start": 11,
    "end": 40
  }
]