I had this issue too, I don't think it's a bug. It just meant to give the user a feeling of boosting up, because the Solo II has a very small heater and tiny airflow comparing to the strong portables (TM/TP80/FW7/TB) kinda "turbo" or so.
so the User Experience get better. you never see this issue with 70W vapes, and i am sure Arizer use a reliable PID internal controller etc', It's not a bug. I am 99% sure.
Other option: It is meant to "preheat" the glass stem before the user inhale, again, small heater, needs to boost