Required properties on nested objects doesn't work

[bhch]

To reproduce:

Schema:

{
  "properties": {
    "object1": {
      "type": "object",
      "properties": {
        "prop1": {
          "type": "string"
        }
      },
      "required": [
        "prop1"
      ]
    },
    "object2": {
      "type": "object",
      "properties": {
        "prop3": {
          "type": "string"
        },
        "object3": {
          "type": "object",
          "properties": {
            "prop4": {
              "type": "string"
            }
          },
          "required": [
            "prop4"
          ]
        }
      },
      "required": [
        "prop3",
        "object3"
      ]
    }
  },
  "required": [
    "object1"
  ]
}

Test data (blank required fields should be invalid):

{
  "object1": {
    "prop1": ""
  },
  "object2": {
    "prop3": "xxx",
    "object3": {
      "prop4": ""
    }
  }
}