Hi, dave,
I had the extractor on for all the demos; occasionally you saw dust build up at first because I forgot to turn on the extractor (my brain sees the hose and thinks the extractor will turn on when I power up, but not the case with the cordless). I didn't get much dust on the cuts; lots of chips, though, especially on long cuts since the downstroke ejects them out the bottom.
I'm wondering how you are getting dust accumulated in front of the splinter guard even with the chipguard down and extractor on. It would be difficult for it to get dust there with the chipguard down. Maybe this weekend I can find a stack of scrap ply or waferboard to try it out. My demos were all on Oak hardwood, 1", 2" and 3" thick.