It's because Stencyl font system is silly!!1!1
Or rather, from Stencyl's point of view, each character is a bitmap of a rectangular shape, and drawing text is based on placing such bitmaps one after another, assuming the bitmap width as a letter width. With such system letter ornaments might causes the bitmap to widen, and thus letter appears to be wider from the Stencyl's point of view. It's particularly visible in the case of l/p gap, where letter L has an ornament on the right at the top, and then there's letter P which has ornament on the left at the bottom.
I'm not sure how that could be fixed, though. Sorry. >.<