thank you for pointing out the memory leak. You are right this is a bug.
I fixed it now in a way that the data is deleted inside the FairWriteoutBuffer. No additional delete is necessary in your code.
This is not the most elegent way. I would have prefered to leave the deletion of the data to the one who created it but the I would have to call the constructor of the data to create a copy which I cannot do in a base class.