I have a problem with the flame engine across different projects. The flames seem truncated past a certain point. I thought I might just have the wrong settings, but I downloaded the demo projects here, and this is what rendered (something like 40-60 frames in, so the flames had time to rise):
This happens with every flame simulation project I make, including using the default Quick Smoke effect. Is there some setting in the User Preferences causing this? I tried it on Blender 2.68 and 2.71 and got the same results.