Drop tank suddenly loses a lot of fuel

[virgo47]

 This was originally mentioned in this thread, but I believe it's a bug:

Original observations:

I've experimented with the drop tanks during the last few days and they are definitely a bit peculiar. I've written a script to see the fuel level in messages regularly (only overall, but better than nothing) to see whether the fuel somehow disappears or what. I always burn a bit of left-wing tank to get around 75 mark and it never gets to F, so I hope there is no problem on this front. The mission is my custom free flight and the stories vary:

• I've flown ~angels 20 on the left drop tank, I switched to the right tank drop tank and lost fuel pressure within seconds, although there was no chance I spent the whole fuel. Repeated on at least two flights, no idea what was wrong. (I have no info on the fuel level for these cases, it was before I added the script.)
• I've active-paused the plane after the mission start at angels 6, fuel 157% (100% is for full internal fuel), went over all the tanks, starting with a bit from the wing left, then the combats one after another... fuel pressure dropped when expected based on the fuel %, I switched through all of them and went all the way to 0. The plane "flew" for over 5 hours, no problem. (I used time accel of course.)
• I went over Caucasus again, ~angels 30, used the both left and right drop tank just a bit, then switched to the right drop tank for good when I was ~140% of fuel. The missing 17% went a bit from the left wing and both combat tanks. Neither of the combat tanks could have been empty by this time, it's mathematically impossible. The fuel reported going down all the way to 92%... it worked like there was some kind of interconnect between the drop tanks, because the moment the fuel pressure dropped, I switched to the left combat tank - and it was empty too!

I have no explanation for this behavior, the only normal case seemed the experiment in active pause. I don't know how altitude is involved in all this, reportedly the altitude can make the engine management harder, but I guess you want to use drop tanks first even when you escort bombers in high altitude - and you probably want to fly high to fly further, but I'm not an expert on this.

Later test with track and fuel message each 10s:

I've made another test, this time at higher altitude, although I'm not sure how important that is.

1. First I went for active-pause test and accelerated time, no problems at all, switching went exactly as expected. Start at 157% of fuel, switch to left combat tank at 152%, then - as calculated and expected - fuel pressure dropped around 123%, so I switched to R combat tank, and then around 95% (first 5% went from the left wing tank) I switched to internal tanks. No problem.
2. Second time I decided to fly actually fly it and also switch more often from tank to tank, but make notes what happens when. To my surprise, things went wrong quickly... again, around 152% I went for L combat tank, then around 143% I switched to R combat tank. I lost a plane for a moment, but I don't believe the maneuvers were that excessive, but... suddenly I lost 50 gals in 10 seconds:

There is nothing in the Score window, I wasn't sure about some malfunction... I made and checked the track again, whether I'd see anything in those moments... nothing obvious in an external view. But 50 gals were lost. Strangely, from the gauges it seemed like some internal fuel was lost as well.

So, naturally, I suspected the maneuvers. I restarted the mission and tried pretty crazy things... but I couldn't replicate it.

Track file is attached.

p51d-lost-fueltrk.trk