For me it always seems to change the font from whatever was built into the PDF (rendered just fine in any PDF reader) to a random system font which completely breaks the spacing, making different parts of the document overflow into each other
That is always going to be a problem with editing pdfs with embedded font information--if you can't match the font, you will screw up the layout. Even if you can match the font, you'll probably still screw up the layout.
