It’s been a while since I looked at it, but I’m pretty sure what it is is that stamina is regenerated when you hit the combo button before the moves consume it, which is why you’re always down the full move amount at the beginning of the second turn, as well as not getting full regen if the amount missing is less than the regen amount. (Despite this, the amount you can spend on moves is still limited to the pre-regen amount.) I’m not sure how that interacts with symbiote form—probably depends on the internal ordering of when the form triggers, which might be after stamina regen?