Hmm I can see many spaces.... but which one is causing the problem for you?
OK I see it. This is very strange, it seems like a problem with your Joomla template but as you said - when you disable JoomlaComment, it goes away!
Could you first do us a favour and try switching to the 'modern' template in the JoomlaComment settings...? See if that get's rid of the space. If it is gone, tell us what JoomlaComment template you'd
like to use (the one you've got now) and i'll look at it's code to test and find the cheeky buster.
[Technical Details: Observing in Firebug, for some reason there's a Line-Break just before the 'contentheading' <h2> (that is, the title of the article) and I don't know where it's coming from.]