Code coverage excludes not working with angular-cli

[PikaChokeMe]

I'm using karma-instanbul-threshold 0.4.0 with
angular-cli: 1.0.0-beta.25.5
node: 6.9.1
on os: win32 x64

I'm trying exclude a single file from failing code coverage reports.
I've tried adding it as

istanbulThresholdReporter: {
  excludes: [
    './src/app/core/services/guard-services/iframe-unload-guard-service.ts'
  ],

and running ng test --code-coverage
But my build still fails with Low Coverage: app/core/services/guard-services/iframe-unload-guard-service.ts 24.24% of 75% lines

Is this functionality currently broken, or am I doing something wrong?