All blocks from OpenBlocks mod with inventory cause plugins who listen to some events to break:

Events onInventoryOpen or onInventoryClose:
getInventory().getHolder() is always NULL

Hello.

Please be far more descriptive when giving bug reports.

Firstly, what exactly is onInventoryOpen and onInventoryClose? These do not seem to be forge methods.

Secondly, getHolder() is also not a forge method, nor part of Minecraft.

Given that, I'm assuming you're talking about bukkit plugins here. We do not support bukkit.

My bad, I posted on the cellphone couldn't write as long as I wish.

It is a bukkit event, all blocks with an inventory seem to not to trigger the correct events, the holder is the block instance, for example "DoubleChest" or "BlockState" which is used by all the Plugins used for data logging or anti-grief purposes.

As the mod doesn't support bukkit you can close this issue and thanks anyway.

Leave this open for the time being. Maybe can look at it as low priority (it might be a quick win)

Then just in case I leave here the kind of error it gives (was able patch the anti-grief plugins so that's the only one we get now):
http://goo.gl/7LYk9B

Found out something else: XP-Bottler with a Hopper also causes server crashes (we are running plain bukkit FTB Monster), basically the same issue:
http://pastebin.com/D5Dk7vZC

Looks to be a duplicate of #323

Confirmed, the hopper crash was a MCPC issue and its fixed, the other one is not related.

We probably can't fix anything on our side. Also, MCPC+ is not supported.