since commit, 7e94e65a1ca (SPIGOT-3845) more entities remain activaded  on a empty server.  

With players online, there is also a above normal increase of active entities, which results in a decline of server preformance
When switching back to a older build (commit 3a482bdd400) everthing is running fine again.

Tested with spigot commit 3aT482bdd400 (27-FEB) agains 7e94e65a1ca (7-MRT) and later (using only plugin essentials OR clearlag to check entities !! )

It would be nice if someone can confirm this strange behavor.