Paul mentioned a bug in the HTML interface of my firmware. Quickly checked what was wrong and released a new nas.web code. Upload this firmware and the issue is solved. Folders created as shares are now deletable again. Somewhere on the road deleted that line. I also updated the whole release package for you so that this failure is not happening anymore.
Thanks for your worthfull comments. I encourage anyone to improve my HTML ;-)
update: new version in the landisk folder. I added the $ character to be allowed to be used for hidden folders. Also added . but that will not cause the device creating hidden folders in FTP ;-)
note: nas45-guifix.web removed and replaced for nasb-update-r5.web for those who only want to have these new features in the web interface. (no need to update kernel / loader)