When I follow the exact same procedure to do a completely new installation of Sync onto a completely new Raspbian (Jessy) installation, it works 100% fine on a Raspberry PI 2, though fails as follows on a Raspberry PI 1:
Setting up btsync (2.3.8-1) ...
Job for btsync.service failed. See 'systemctl status btsync.service' and 'journalctl -xn' for details.
invoke-rc.d: initscript btsync, action "start" failed.
dpkg: error processing package btsync (--configure):