This has been touched in a few other threads but I'll put my observations here so that I'll not derail the others. Basically I wanted to check if we can find some form of an workaround before this is fixed.
The most usual situation (and the one that interested me) is when you give an explorer the command to explore sector X and it does so until it needs to refuel; then it forgets about it's mission and goes idle. So i did the below tests:
1) gave the command to explore sector X then queued up 10 "explore the nearest unexplored system" commands as this was the only remaining option (quite tedious, even more so considering that if this works you may need to do it with dozens of explorers). The ship managed to explore system A and B before needing refueling, then refueled, then...returned in B and consumed all of it's queued missions there. Observations here:
1.1 I think Elliot also mentioned this some time ago but an explorer does not fully explore a system on it's first pass (especially in the early game when sensors have not that much of an extended coverage) so I'm not surprised that it returned to B after refueling but 8 more missions consumed there is too much.
1.2 Clearly the "explore the nearest unexplored system" command takes into consideration the current position of the ship not the position it will have when the next queued mission will kick in so you can queue an infinite number of these missions and they will not have any effect . It would have been a boring workaround too.
2) gave the command to explore sector X then immediately put the ship on auto. I did this hoping that after the inevitable refuel the ship will auto explore the sector; same routine until the refueling and after that a momment of consideration and the ship began to explore on it's own, even systems outside this sector. So when put on auto it will forget (as expected i think) the previous manual command...but again, only after refueling -> you'll see why this is important.
3) gave the comand to explore system A then queued for exploration systems B..F (all these as "explore this unknown star" command). This time it behave better, even after refueling it completed the queued mission and moved to the next one. At some point it finised with D and started to E then stoped because it reached the need to refuel point and went back to refuel. Then it went to F and I was begining to think that this is broken too as it obviously forgot about E. But it returned to E after F, completed all missions and stopped (F was closer after the refuel....the AI is very smart is seems only after refueling :) ).
A) Even if the "explore sector X" is a superior and much needed option it seems to work badly, aside from the above mentioned reasons there is also the fact that when set to this the AI will explore as fast as it can as many stars as it can in that sector and it will explore them partially. While when you set it to explore on a system by system basis it will fully explore a system before moving on.
B) We could use option 2 above and monitor the explorers so when the auto kicks in after the refueling and the sector exploration is forgot we could manually reset it and then put it back to auto. In combination with more fuel cellls to make the autonomy of the ship greater it could work without much micromanagement.
C) The third option is clearly better (the AI on auto may function in the same manner) but it involves more micromanagement from us; this is not so bad in cases when we really want a particular area of space explored.
...Igniting stellar cores....Recharging reactors...Recalibrating hyperdrives....