In this most recent snapshot I attempted to use barrier blocks and lava to create flames fanning behind a rocket the whole system was designed to use a single block of lava to create the effect so that the rockets could be turned on and off with a piston. When I turned the rocket on however and the lava began to flow down the barriers my fps dropped as the lava spread eventually freezing the game altogether. After several attempts to make my rockets work I went back to the 1.7.10 version of the game and created the same system using stone instead of barriers. To my surprise the lava spread without causing any significant fps drop. After doing several more tests in 14w34d I discovered that any lava spreading lead to an fps drop averaging 10 to 15 frames per changing section of lava. Meaning that if I run 60 fps and place 4 buckets of lava on the ground I will get 0 fps as soon as they begin to spread. Because this sudden lag is not present in any other version of the game I have been lead to believe it is a bug. If someone else could help confirm this I would greatly appreciate it.