Elasticsearch highlighting on ngram filter is wrwong if min_gram is set to 1

Elastic Stack Elasticsearch
1

So I have this index

{
  "settings":{
    "index":{
      "number_of_replicas":0,
      "analysis":{
        "analyzer":{
          "default":{
            "type":"custom",
            "tokenizer":"keyword",
            "filter":[
              "lowercase",
              "my_ngram"
            ]
          }
        },
        "filter":{
          "my_ngram":{
            "type":"nGram",
            "min_gram":2,
            "max_gram":20
          }
        }
      }
    }
  }
}

and I'm performing this search through the tire gem

{
   "query":{
      "query_string":{
         "query":"xyz",
         "default_operator":"AND"
      }
   },
   "sort":[
      {
         "count":"desc"
      }
   ],
   "filter":{
      "term":{
         "active":true,
         "_type":null
      }
   },
   "highlight":{
      "fields":{
         "name":{

         }
      },
      "pre_tags":[
         "<strong>"
      ],
      "post_tags":[
         "</strong>"
      ]
   }
}

and I have two posts that should match named 'xyz post' and 'xyz question'
When I perform this search, I get the highlighted fields back properly

<strong>xyz</strong> question
<strong>xyz</strong> post

Now here's the thing ... as soon as I change min_gram to 1 in my index and
reindex. the highlighted fields start coming back as this

<strong>x</strong><strong>y</strong><strong>z</strong>

posxyzt
xyz
questioxyzn

I simply cannot understand why.

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2

using Elasticsearch 19.2 btw, also want to point out that if I change from
using nGram to EdgeNGram (everything else exactly the same) with min_gram
set to 1 then it works just fine.

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