On Thursday 19 February 2015 at 16:48:03, Mathias Behrle wrote:
> In case they should be needed by some
> legacy module and the lines should be considered necessary, at least there
> could be a added a test to not add them twice.

Yes, this is the way to go once we find out.
I believe the next steps would be: 
* see in hg history when this was added.
* check out at which other place the headers are set currently.
* check f the behaviour of this module changed in the past.
* (maybe) try an elder verison of round. Or try the oldest.
* (optional) write/extend a test case that checks for double header lines.