spark bug

Hi, I apologize if this is posted in the wrong place. The only place I was able to find for spark was in japanese.

whenever I export my projects as a PDF, I just get a black screen when I try opening it. I asked my friend, and he says that there's bogus alpha channels in the document. I also notice that exporting to PDF creates a much higher resolution copy of my document. There's usually no difference between the PNG and JPG exports. They're both low res. Why are both of these happening?