So I was trying to get back from Duna to Kerbin, and the maneuver nodes didn't make sense. The only way I could get back to Kerbin according to those was to go prograde relative to Duna's orbit, which is of course wrong.
This is how it looked:
After I accelerated as the node suggested, it still looked like it would actually work:
But as soon as I left Duna's SOI, the orbits corrected:
(I instead made an educated guess on how much to accelerate in the correct direction (retrograde compared to the planet's orbit) and managed to get back to Kerbin, but this is obviously not expected behavior)