Sounds run of the mill. I think what happens is that as the trichomes vaporize, the plant wax that comprises the trichomes "melts" and becomes a bit sticky. A few hits farther down the line, when it starts to fully brown, it stop sticking for me. I assume this is the point where the plant waxes have vaporized and broken down enough to not be an issue. I get the same thing happening with the first hit of a trench, I'll twist and turn and shake it like I'm having a seizure, but there's a layer of herb at the bottom touching the screen that seems to stick. What I've found is that if I give it a bit more juice on the second hit than the first, it "unsticks" itself. My old and new box does it, regardless of the strain I use. Like I said, after the second or third hit it stops being an issue. I have not noticed any screen damage occur because of this. In fact, when I can "afford" it, I like to load trenches of just kief. Takes less hits to get me going than it does with flower, let me tell ya...
As for material getting into the air channel, yeah that's due to the recessed form of the air channel. I think it was OF that told me that you can place a small strip of electrical tape at the end of it closest to the trench and it will prevent about 95% of the material from getting through there, but it doesn't seem to restrict the air flow when I draw. This is how mine was configured.