TypeScript decorator reports “Unable to resolve signature of class decorator when called as an expression”

同樣的兩段代碼，同樣的vue-property-decorator，編譯器報錯。不清楚是我哪里有問題？

  "dependencies": {
    "vue": "^2.5.2",
    "vue-class-component": "^6.0.0",
    "vue-property-decorator": "^6.0.0",
    "vue-router": "^3.0.1"
  },
  "devDependencies": {
    "css-loader": "^0.28.1",
    "ts-loader": "^2.0.3",
    "typescript": "^2.3.2",
    "vue-loader": "^12.0.3",
    "vue-template-compiler": "^2.5.2",
    "webpack": "^2.5.0"
  }