ellisian

Confirmed. One player breaking a wither skull causes the server to crash. Operators in creative mode are able to break skulls with no issue. It's just players in survival mode that cause the crash.

This issue is still present in 15w33c for terrain generated spawners. The spawners I'm looking at were generated and working normally in week 32 but stopped working in the new snapshot.

In 15w32c the "Tried to add entity..." message no longer occurs. Now the server log is being spammed with "[Server thread/WARN]: There were X entity removals pending!". So far I haven't experienced any issues with animals or other entities disappearing. Except when breaking item frames – that causes both the frame and it's contents to vanish.