After evaluating the full web stack and disabling/enabling individual layers, was able to narrow it down to a bug in LiteSpeed - their Apache alternative. Apparently a common occurrence for their current version:
http://www.litespeedtech.com/support/forum/showthread.php?t=5870
As opposed to downgrading as the forum member did, I completely removed LiteSpeed and will most likely be loading Varnish in its place. Marking this as solved and tagging with "LiteSpeed" for the benefit of any of its users experiencing similar issues.