Can't move when flying up with the classic controls

Using the classic controls, after I swap jump and sneak, I cannot move when flying up. In the past before the addition of new controls, the fly up button is on the right side together with the fly down button. I can move by clicking the direction buttons on the left while pressing the fly up button on the right. But now the fly up button is located on the left, as I can only press one button at one time with my left hand, I cannot move when flying up, but only when flying down. The fly up button should be placed on the right side. Even customizing controls dont work. Please correct this logical bug.