First off, I don't keg yet....but
When you transfer from the primary to the secondary, I have found that you have a tendency to stir up the trub a tiny amount and re-activate the yeast a little bit.
Almost everytime that I have done this, I get a minor amount of activity in my airlock on the secondary. Then, after a few days, things continue to settle out and "conditioning" continues. I have a few 5gal glass carboys, they were not terribly expensive.
You could try, maybe leave it in the primary a bit longer than necessary to settle out the brew even more before you transfer to your corny.