Ok, kind of a confusing title, but here's the step by step:
Choose a zone to adventure a set number of turns in.
Select a number of turns (X) higher than your current amount available (Y).
eat/drink/whatever to gain more turns, higher than the number you set.
Begin adventuring.
The number of turns that you will adventure is Y, the current max you had when you set the number, even if you have more than that when you click to adventure.
Basically, it should check if you have enough turns when you begin adventuring, but it's checking early and setting the number then.
Choose a zone to adventure a set number of turns in.
Select a number of turns (X) higher than your current amount available (Y).
eat/drink/whatever to gain more turns, higher than the number you set.
Begin adventuring.
The number of turns that you will adventure is Y, the current max you had when you set the number, even if you have more than that when you click to adventure.
Basically, it should check if you have enough turns when you begin adventuring, but it's checking early and setting the number then.