Firstly I would like to thank the devopers, I love JDownloader!!! Also the latest update seems to have fixed filesonic download problems!!
I think I have a workaround for fileserve premium users in the UK. It's quite simple really and save you having to give each portion of your download your undevided attention.
Increase the number of downloads / connections (not sure the difference so I do the same for both) to the number of files you are downloading from fileserve
Activate the download for all your files at the same time, and go to the 'Settings' tab and make sure that your Fileserve box stays checked.
Once all files are downloading, and fileserve box stays ticked (and FS appears the very bottom left hand corner of the download tab) it is safe to leave your computer.
When you wake up in the morning, all your files will have downloaded!!
Seems to stay stable if you throttle the download speed too!!
Maybe one day the developers will be able to fix, as IDM (Internet Download Manager) seems to be happy working with fileserve on the same computer (however IDM doesn't do filsonic.)