I can confirm this. I run a E3-1245v2 server with about 40 players on. At the end of 1.5.2 I never came under 19TPS. Now in 1.6 I have many lag spikes. Usually I run at 20 tps but then a few zombies get stuck and I get a massive spike which lasts until they are dead. Here is a short sample of such a spike.
http://aikar.co/timings.php?url=5882102
Note that there are only 1000 activated entities. I used to run double that amount without any problems.
Relogging does not fix the issue for me Daniel. When I do it stays exactly the same. Only hitting it seems to have an effect.
This issue dates months back :O is this really that hard to fix ?
I would really like to see it fixed. I just generated a 1.5 nether and it looks really awful because of this.
I really hoped this was fixed but it is back again! Added a picture of a black tree.