Problems with flame simulation

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.

If you mean the edges of the flames as below, that’s the boundary of the smoke domain object

The smoke domain is about as high as it is wide, and adaptive domain is enabled: This is (supposedly) the same project file used to make the video on that page. And again, this happens with several projects.