Contact sync: bug or feature?

🍱 Features & apps
1

Thunderbird 45.4.0, Lightning 4.7.4, SOGo Connector 31.0.3, Nextcloud 10.0.1, Ubuntu 16.04.1, Apache 2.4.18

Syncing seems to work, but when a contact is being deleted remotely, it will not be deleted from Thunderbird after syncing.

Bug or feature?