Xerca

I couldn't reproduce the bug with vanilla client and server but then I tried it with only forge (no other mods installed) and it happened again. So, I think it can be a forge related problem.

This happens on my server sooo frequently that it has become extremely annoying for everyone playing in the server. Sometimes players see the same place sink, sometimes different places. There are some specific parts which almost always sink. If there is a sign on the sunken part I think it also says "Unable to locate sign at x,y,z". By the way, it started the moment I updated to 1.4.6, so I'm sure it does something to do with that update. It actually fixes if you jump into the fake hole and logout-login but to only make another part of the world sink. If you by plugin mean mods, then my server has forge and a mod that uses forge which does nothing to do with this kind of thing. I also have lots of screenshots but they all show the same thing - a random chunk that seems to be 10 blocks under where it needs to be.

This (when you think an item is taken/placed but it actually isn't) happened to me lots of times and it is really annoying when I don't notice it soon after, but I'm not sure if that happened when I clicked more than once on the chests. I hope this is the only bug that causes this.