It looks like it's selectively adding <p> tags. For example, on the post Registration Turned Off, it's correctly surrounding your post text with paragraph tags.
In the post below that, where you feature a video, there's an opening <p> tag, no closing <p/> tag and not enough "air" between the bottom of the video and the Tag section.
I suspect that you normally use the WYSIWYG editor to compose your posts, but that you turned it off to add the video and its post text, correct? That may be why you are having that problem. So for instances where you have to add a video and have the WYSIWYG editor turned off, you'll have to remember to add those opening and closing <p></p> tags to your post text.
Unless there's something else that I'm missing.