Rocket trip distance is calculated incorrectly

Petroleum rockets seem to have their available range listed 1 tile less than it should be (most of the time?). On the attached screenshot the rocket says "range remaining: 6 tiles", but trip distance is only available 5/5.

Note that the correct value should be indeed 6 tiles (540 fuel, 90 fuel per tile), see another attached screenshot.hen 

Quite dangerously, sometimes a rocket might say that it has N remaining tiles, its trip distance says x/N. Then the rocket moves one tile, it says Range remaining: now says N-1, but the trip distance says x-1/N-2. This means that a rocket might no longer have enough range for a return trip, because it has lost one tile of trip distance, and it's the value that actually matters from the gameplay perspective.

Note that most rockets are affected, but not all. Here's an example of another petroleum rocket that seems to list its distance correctly: