Me 110: Tank switch & 1-axis AP

[Redroach]

After my first rather lengthy flight in the Me 110 (140 mins), I'm a bit confused with the tank selection switches. The switch on the front panel to select which fuel tank quantity should be shown, seems to work fine. But the switch on the side panel, where you (presumably) actually switch from tank to tank (Front left, F/R, Back left, B/R) seems to be reacting a bit strange from my pov.
At some point, I've completely drained F/L - red light on the panel went on, the gauge showed empty. All in order so far, so I switched to the next tank - F/R, if I remember correctly. But later, the light for B/R went on, despite if selecting to show F/R on the dial, it seemed to be full. And, actually, I started to lose power, so I presume there could be something the wrong way round. I haven't tracked it piece by piece, but the final situation was: Light on for F/L and B/L, Gauge showing 0 fuel for F/L and B/R, and engines NOT losing power (i.e. tanks actually NOT empty) for B/L and B/R
Can somebody shed light on this? Or could it be declared a bug?

As for the second point, I'd really appreciate it if somebody could give me a short introduction for that shiny 1-axis-'course mode' autopilot in the Me110. I'm not really sure how to use the knobs and switches. After 'testing' around rather randomly, I've settled on a course that fit my desired one quite well, but the read-outs were rather awkward:
-Magnetic Compass showed 68° (Yep, I'm aware of magnetic N vs. geographic N )
-'Daughter' Compass showed 71° (might be irrelevant with respect to the AP)
-upper dial in the AP controls showed 59°
-lower dial in the AP controls showed 55°
So, somewhere 'in the middle', I came home with that, but I'd like to understand it a bit better. It seems to be a neat tool, especially for the long channel transits