Just to tell you that I've added this cosmetic issue to User:Noreplyz/UCP with a link to this thread as containing a workaround. In fact, as Andrewds1021 has said, if you add a <div> tag around the infobox, that would avoid the creation of those empty paragraphs.
<div><infobox>
...
</infobox></div>
A simple div, with no class or style, should not mess with the infobox floating attibute and margins. But if you do use it, it would be a good idea to check a couple of pages where that infobox is being used, just to verify that every thing is OK.