I saw this behaviour also earlire but decided to wait for the latest installers for all three buses.
I now have followed Daves instructions how to unistall and install in right wway so everything is fresh.
I start fuelplanner and choose advanced tab.
I make a route from ESSA to ENGM. It is 208nM
Fuel planner automatically calculates and comes up with a amount of fuel.
If I after that increase "Alternate distance" by one step at the time with the arrows the fuel calculated sometimes increas and sometimes decreas even if every click is 1 nM miles longer.
The same behaviour happens on all buses.
Alt distance 187nM 16997kg (A330)
Alt distance 188nM 13125kg (A330) (Less fuel but 1 nM extra)
Alt distance 189nM 14039kg (Now increas again)
Alt distance 190nM 14953kg (Increas again)
Alt distance 194nM 13824kg (Now less than it was on 187 nM but 7nM longer)
Maybe it is me that do not understand the logic behind alternate distance.