Exploring a large cave system that my strip mine encountered around y:40 began to induce severe framerate drops and freezes. A unique 'slow-motion' effect takes place as the framerates and memory return to normal, only to be affected again shortly after if I were still in the area. Framerates would drop from 120 to 40 to 0 (readable in between screen freezes), CPU utilization on one (of eight) cores would spike from ~20% to ~90%, in-game memory would spike from 200 mb to 900 mb when this occurs. The issue occurs in the same general area, with no redstone or running water (cave cleared of water sources) and nothing but generated terrain. It can occur while moving or standing still. The internal server appears to continue to run, as mobs have attacked me in this crippled condition. Leaving the area will resolve the issue, and no issues will be present when visiting the same X, Z coordinate but on the surface.

Immediately preceding the issue is a series of quick freezes that do not appear to show any debug output. They are followed by the aforementioned issue. Viewing the debug console during the 'event', the 'Clientside Chunk Ticking' reports warnings of over 4 seconds (4000ms+). These skipped ticks coincide with the freezing of the framerate.

Steps to recreate are to simply revisit the area of the large cave system of this seed.

Edit: The seed is -994244704 and the area affected is near 82,33,429.
Edit: Found ravine 37,29,416, occurs here as well
Edit: -16,83,162 as well

Edit: Recreated the same world (same seed -> 'xcentrik4') in 14w05b, continue to see "Warning: Clientside Chunk Ticking took XXXX ms"