Getting a block in the world stucks the server

Recently, after the release of 1.4.5, our servers have been facing getting stuck every so once in a while. After profiling it for about every time it crashed, we've found that the crash is caused by getting a block in the world. Presumably by a never ending loop.

http://puu.sh/1wpOJ/7fe2595067111b0ec74bdc10a0a632f5

Previous profiling sessions pointed at the generation of ores.

Which is, on it's own strange, since we pre-generate the map to even further then players can get due to a forcefield holding them back.