Now that 1.1.3 is out, I have tested on a fresh KSP install with default settings, as well as with my preferred settings reinstated. I can no longer reproduce this bug.
I see no direct mention of this in the patch notes, but Squad did fiddle with the orbit code in several ways. Whatever they did works for me.
Marking as solved unless/until someone reproduces this in 1.1.3
Jens Lyn IV's post in [Resolved] Orbit Line Disappears Upon Achieving Escape Trajectory [1.1.2] was marked as the answer