That's normal. The only way to fix this is for us to add some form of antialiasing - which is on my list of things to look into. I'm not 100% sure, but if you're exporting a mix, I believe that you could also use this trick: double the width and height in the MixEmergency Export window (e.g. 640 x 360 would become 1280 x 720) and then reduce the size in the custom export section (i.e. don't use a preset, and set the size to 640 x 360). Be warned though - it will take a lot longer to export. I would recommend trying this out on a short test video first.
