This has been occurring on our server aswell. however i did testing on my own end. I reproduced what my server owner did before the bug started. I am running a clean install of the tekkit server and failed in reproducing the bug after emulating what the owner did. the only plugins we run on the server are tekkit restrict,worldguard,worldedit,LWC <-- LWC is my possible candidate for the bug.
Also a new block was discovered. It seems RedPower Monitors also cause the crash on our server. I'll get you guys a crash log of the file shortly. it might help.