I knew if I fiddled long enough I might find out something else....
Selecting the output plugins settings and disabling the K8062 and re-enabling it and the LED blinks very fast indeed.
Like this it'll control only the first 7 channels regardless of how many channels you had set and appear on the output page.
So...on startup of DMXControl it does all 512 by default, on disable/enable it does 7.
So number of channels does appear to be being set...but not as you think they are!
This test was consistent between restart of the app. and powering-down/up the K8062.
I've tried also this on Windows XP and Windows 10 - both on 2.12.2 - it's consistent.