Question about test cut

As I mentioned in my intro I bought a PC VS Combo from amazon and ordered the inexpensive 24 bit set from Holbren. When the bits arrived I tried it out. It's been awhile since I used a router, the whitewood scraps I tried it on were short, the clamps were big, but I seem to remember how to set the cut depth (the scaled ring seems useless for that). I tried a couple of 1/4in deep 3/4in dados on the 1x2's using another scrap for a backing board. First try I did not have the clamps tight enough and the boards slipped so I got and angled dado. Second cut went alright but the clamps were too close for comfort (Note to self: if you need to route short pieces, route them first then cut to length).

Now here is my question (thought I would never get to it, heh?), I got whiskering at the top edge of the cut; what causes that? Was the new bit dull? Was I feeding too fast, too slow, or too deep? Was it just a characteristic of the wood? Or something else?