There is an error in the vue.js documentation for the .sync modifier you can find here:
https://vuejs.org/v2/guide/components-custom-events.html#sync-Modifier
It states, that you should use a kebab-case event name for the .sync event:
That’s why instead, we recommend emitting events in the pattern of update:my-prop-name. `
This is not correct. because the event must be camelCased to work properly.