I have tested this on a Samsung Galaxy Note 10.1 and I can't see any changes. Groups still persist. I also don't understand how this should work theoretically:

* GroupMembership is a data row (i.e. accessible via `dataURI()`), so why should this additional newDelete() change anything? All data rows are already removed by the first newDelete().
* Also, as fas as I understand, groups are not handled on the "raw contacts" level, but one level above on the "contacts" level. This means that DAVdroid (which is responsible for syncing *raw* contacts) should never delete a group, only group memberships of raw contacts. However, it would maybe a workaround to delete groups without members at the end of a sync (although this would be the responsibility of the Conctacts provider).

Does this really work for you? Can you provide additional details as the used server, Android system, maybe database dumps?