Just did a group download task (instant deploy) with SVN 3575 - and the basic snapin behavior seems to be fine now.
The snapin tasks are displayed and applied correctly. To put the computers in the domain also is faster (tried the new fog client with this svn)
Thank you very much!
(I hope next week I can test a scheduled group download task run and the the behavior with the the deletion of a download task when deleting all (to a host) connected snapin tasks)