Well, now I'm confused. Your description is straightforward enough, it was easy for me to test. But I get a piano sustain interruption on "L". I can't tell if it's exactly the same as on start/play, but equally distracting. I could make you a recording, but I'd have to record outside of Cakewalk because- well- CW doesn't know about the problem, it's in the outside world so to speak.
In lieu of a software fix or effective workaround, I see only 2 ways around this. 1) What I've been doing- is leaving "air space" around starting the track- silence, no sustained notes. Doesn't sound right to me, but at least I feel and sound like I'm in control- though not really, software is controlling the music instead of other way around. Or 2) add the whole rubato section to the beginning of the track, with enough audio or visual cues for me to play it with close enough timing every time for me to be in the right spot when the "real" track (with drums etc and strict timing) begins- again inhibiting but I can learn to perform it accurately. Again one might ask who's in charge- sounds like it's CW. Artistry is only possible where the technology permits. Most of us musicians would rather concentrate on the music when we can and not struggle with operating systems, settings, drivers, and such.
...On further thought, a 3rd option- 3) pick a spot as close as possible to the end of the rubato section where a moment of air space or silence may seem more musically natural or acceptable- for the track start. Carefully craft the beginning of the track and rehearse the transition and track start until it's effectively flawless. I can make it work. More effort than it ought to be, but it'll fly.
Thanks for your attention and help.