Dynamic Matrix: "Default row value" dialog doesn't allow changing the default value specified in the JSON schema

[JaneSjs]

Consider the following survey JSON:

{
 "logoPosition": "right",
 "pages": [
  {
   "name": "page1",
   "elements": [
    {
     "type": "matrixdynamic",
     "name": "question1",
     "defaultValue": [
      {
       "Column 1": "1",
       "Column 2": "2"
      },
      {
       "Column 1": "3",
       "Column 2": "4"
      }
     ],
     "columns": [
      {
       "name": "Column 1"
      },
      {
       "name": "Column 2"
      }
     ],
     "detailElements": [
      {
       "type": "text",
       "name": "question2"
      }
     ],
     "detailPanelMode": "underRow",
     "choices": [
      1,
      2,
      3,
      4,
      5
     ],
     "cellType": "text"
    }
   ]
  }
 ]
}

If you define the default matrix value:

The Set default row value dialog doesn't contain any rows: