It's picking up the line-height from #content. You'll need to be a little more specific. You already have a #content h1 {}, if you add the line-height to that it will work.
Related: I have noticed a very annoying case in which the line-height doesn't work no matter what. It probably has a reason, but instead of searching the "why" I found the "how" to make it work quickly.
Can anyone from the community try with their firebug that why line-height is not working for class 'headlineleft' i.e. the post title. The sample page is http://www.gtricks.com/google-tricks/google-fail-dead-products/
I wish there was some kind of thanks button in vanilla forum so that i can show my gratitude.
(The "1" can be whatever you want, of course)