Hi Matthias,
Thanks very much for the detailed report. Tim forwarded this to me and I've looked at the samples you've posted and done some investigation on our own server.
I think something else is compressing your page output and it's doing it at the PHP level BEFORE falcon receives the data and caches it.
So can you please post a list of the plugins you're running and I'll examine the list and try to reproduce this in our lab.
Thanks again for the helpful report.
Regards,
Mark.