As I read the service manual for more inputs:
I found this post with a few images:
http://www.kawasakiversys.com/forums/9-technical-discussion/19534-airbox-backfire.html
So I went down to give it a shot. I turned the sensor down/counter clockwise by a hair (to the left if facing the bike). Started her up. On cold start, the RPM went a bit crazy and shot up to 3k RPM and then settled back down. But something was amiss. I held the clutch and tried to get the bike to move and she just shut down. I think the fuelling was made even leaner?
So I went back down and turned the sensor the other way - up towards the fuel tank (to the right). Then I readjusted the idle to about 1400 rpm (up from 1300). Went up and down by street a few times, and seems like the problem's gone.
Either I'm daft, or Kawasaki has changed things on the 2015 model. I would like to believe I am daft.
However, when I release the clutch to get the bike going, the RPM goes below 1000 and the bike doesn't really move unless I give her a bit of gas. Is this normal?
Going to get out in the morning and start her up to see what next. Might just avoid the trip to the dealership.