Encountered a visual Fuel Bug recently.
If you alter the Fuel loads, for any future Stints, through the in-race Strategy tab, it default changes your next pitstop to that Fuel level.
ie.
Predetermined Set Up and Fuel (Japan)
Stint 1: Soft - 23 litres
Stint 2: Hard - 44 litres
Stint 3: Hard - 44 litres
Stint 4: Soft - 26 litres
Modified Set Up and Fuel, through in-race Strategy tab
Stint 1: Soft - 23 litres
Stint 2: Hard - 44 litres
Stint 3: Hard - 44 litres
Stint 4: Soft - 25 litres
It changed the next stint (Stint 3 in this case) to 'Stint 3: Hard - 25 litres'
Also, if you increase the Fuel for your next stop (Stint 3) it goes from '25 litres' Hard to '45 litres' Hard
Pure visual bug (not tried racing the '25 litres')