I've noticed line spacing problems in some of my posts. In these cases, there was no whitespace between the last line of the post and the footer of my poster (e.g. "Posted by qmechanic...")
I posted my problem in the Blogger Help group and got a very helpful answer. To make a long story short, it has to do with the way Blogger templates work and the issue can be fixed by inserting a strategic paragraph opening tag.
I went through my entire blog and fixed all the posts with this problem. I also fixed a few other line spacing errors, unrelated to the Blogger template.