Problem/Bug Items not stacking properly

I am running the latest craftbukkit and everyone on my server is having this problem. Whenever players grab items from the ground and already have a few of the item in their inventory, it sometimes doesn't stack up properly. So for example: Player has 30 dirt in inventory. Grab 3 more off the ground. Now he has 30 dirt and 3 dirt in separate stacks in his inventory. What causes this? I have updated all my plugins. This is my list:

http://puu.sh/hNmnL/4f0ef5db4e.png

Thanks!
~ A desperate server admin

 

Update: I tried temp removing all of my plugins. Didn't work. I tried switching to an older bukkit version. Didn't work. Items are actually DISAPPEARING when this occurs! My players are becoming angry and I don't know what else I can do. Maybe it's due to lag? (the server is 512 mb and I host 5 - 8 players). Anyone?

 

Another update: I tried deleting all of the player data/inventories too (in case of a corrupted item). Didn't work. Still haven't fixed it.

 

Up.

 

post the logs/latest.log after a fresh startup - you might be having some ..complaining .. plugins that are causing side-effect actions, plus, we'll be able to double-check the versions that are loading, and see if there are other complaints. Paste the log contents on www.pastebin.com and put the link here