Panel Plugin Notiification on Upload Problem

I have a Panel Plugin to upload a file. The template looks like:

  <div>
    <k-button @click="upload" icon="upload">Upload</k-button>
    <k-upload ref="upload" @success="onSuccess"/>
  </div>

That is the default from the Kirby 3 documentation.

The problem is, that the onSuccess event after a successful upload won’t get triggered. There seems to be some event because the standard success notification (the same like on page save) is shown. But my own success method from the .vue file won’t be called.

What can i do to get my custom notification after a successful upload?