The content #000000 that you are getting is actually the font color of your input.
In kupucontentfilters.js, it confuses the attribute 'text' with 'textContent'. The attribute 'text' refers to the font-color of your text while 'textContent' is your actual text input.
I can probably submit this fix to the kupu developers as well.
This patch has been tested with both firefox and internet explorer and works well with both.