Synchronize-non deletion of empty folders

[nac2k]

I use FC 2009.02b on WinXP.

I use it to backup data between my notebook and the external HDD, I usually have the notebook's directory on the left panel and the external HDD's folder on the right panel. I then click on synchronize, followed by compare with the "with subfolders" option checked. Once comparison is done, I click on synchronize and go for "Asymmetric - backup of left side".

What happens then is as follows:
The files on my laptop get copied to the external HDD, as I want it to be, but the empty directories from my earlier backups on the external HDD do not get deleted and continue to remain. I would prefer these to be deleted too and the external HDD to mirror exactly the files and the file structure as on my laptop. How can I achieve this?