The pattern for me at the moment is that mapping planets requiring 2 probes (or low mass 4-probe planets) 'sets' the bug - after that any subsequent planet in the system will be marked as 'Mapped' (and you can check this in the left hand nav panel). However, if you then go on to scan a high-mass six, or a seven probe planet, it re-sets the bug. Jumping to the next system also re-sets the bug for the new system, but if you go back it's still the same. Logging out altogether or to Main Menu does not reset the bug.
Also, if you scan a low mass planet with a moon in close proximity (or vice versa) the image of the probe landing on the target planet is replicated on the companion planet. Amusing as it may be, it's still a bug, and gives us a clue as to how it affects other planets in the system. In other words, it would appear that under certain circumstances the game to set the status of
all the planets in the system to 'Mapped' for graphical display purposes, but in the commanders personal inventory the planet is still 'UnMapped'.
Btw I can't find the reference to this in the issues tracker - if anyone can point me to the right thread, it be grateful - thanks ! For now, I'm developing my memory skills as well