(1) Open up this file from your Joomla install:
components\com_comment\joscomment\
(make sure you use a UTF8 editor such as Notepad++)
(2) Go to line 752, which should have this:
$previewline = str_replace('{PREVIEW_TITLE}', $title, $previewline);
(if it's the wrong line, just search for it)
(3) Tell the str_replace to add a couple of spaces before it, like this small code change shows:
$previewline = str_replace('{PREVIEW_TITLE}', ' '+$title, $previewline);
...notice the --->
' '+ <--- adds a whitespace before the title text on the preview
...that should do it. Of course you can make it three spaces if you like, whatever is in the ' ' it's up to you
I'll have to remember to tell Daniel about this one, I am surprised nobody has reported this one earlier