Headers not sent when using {% flush %}

[GenieTim]

Thank you very much for this awesome bundle!
I just used too much time to find out why none of the configured headers were sent. That is why I opened this issue, to warn anyone here / request change / request documentation – headers do not get sent when using flush(), respectively {% flush %} in Twig.
I am not entirely sure why this is the case though, as, as far as I understand, this bundle already sets headers when retireving the request. Maybe I am wrong. Just wanted to mention this in case anyone else struggles with this issue...

Or is there a workaround?