More info:
Steps to reproduce:

1. Create Server rack item, place it power it etc
2. Place a working server inside of a Rack. (didn't have an OS yet though)
3. Turn on a server.
4. When server is still on, pull it out, push "Off" button.

This is not reproducible in singleplayer, but easily reproducible in multiplayer due to network lag.

I cannot reproduce this. Furthermore, the log you pasted does not mention OC anywhere, making me doubt it's actually related to OC. Please post a full crashlog.

I'm gonna try to recreate these circumstances and post a full failure log, once I get a server running with decent net lag.

@nekoexmachina How bad was your speed connection to the server? I got mine to freeze twice now, no log however (didn't crash, was unresponsive). Running the server on Debian 6 with Java 7

@KJA1582, i've toyed around with lags & stuff. Opis seems to ve the main issue in this bug, not opencomputers. Without opis, no crash, while with opis, about 2 od 10 tries result in crash.
Sorry for wrong bug!

OK, if it turns out to be OC after all, let me know and I'll reopen this for further investigation.

@KJA1582 regarding the freezes, did you have a look with VisualVM what was hanging? If that's OC, please open a new issue for that, and let me know where it hangs, thanks!

I tried this for about 4 or 5 hours, it is very elusive. It could be OC since, theoretically, by trying to shut down a removed server it basically is sender a call to a nonexistent object, which potentially can hang any program.