@mark Oh yes! Indeed now it makes sense. The barber pole is the issue, not the speed, my bad!
And this also answers my question about fuel flow -> I was actually accelerating to mach 0.8 instead of the usual 0.75 so that makes sense now..
Concerning the altitude, I was wondering if for long flights like this one (2h+) you could climb above 30k to save more fuel. It makes sense not to climb farther for short hops, but for long flights...?
Thank you for taking note of this bug and I hope it gets fixed very soon