Invisible Creatures??

Hello i am experiencing a problem since the new recommended build (It might have been since the 1.4 update to be honest)

I am having monsters become invisible and attacks me and other players.
CB: 617

Plugins
Chat-Bukkit: 83
Scrap-Bukkit: 122
HeroChat: 4.8.6
LogBlock: 0.10
NetherGate: 0.54
Permissions: 2.5.5 (The Yeti)
SpawnX: 0.4

There is me and my housemate on the server. Before 1.4 i had 20+ people on the server, around 5x the amount of plugins without these issues. Im really not sure what is going on otherwise i would give you more information.

I know when you log in you can see the creatures, or at least some of them. Then once you die and respawn, you have to relog in to see them again. Very nasty, people saying "Creeper!" and you go running into it because you cannot see it, thinking its behind you.

 

Not sure how to fix the problem but I guess for now just turn off mobs in the server properties file.

 

I guess so, defeats the point of a SMP server really.