WE KNOW THIS IS NOT FIXED IN 13w21b/13w22a/13w23a. PLEASE DO NOT COMMENT ABOUT HOW THIS IS STILL AN ISSUE.
I launched Minecraft Snapshot 13w21a and I jumped into my 1.6 test world. I have flowing lava, flowing water, and an active nether portal all within a few blocks of each other. The flowing water is animated at what I would call the corrected speed, that being the speed that it is animated at in previous Minecraft versions. The nether portal is also animated at the correct speed. But flowing lava is not. Flowing lava's animation makes it look like it is flowing 2x faster than water flowing animation. Also, lava source block animation when it is not flowing is also animating too fast.