0) I had sent a larger fleet to a defense point at the coordinate of attack, had made my attack, and it was now debris there.
1) I send my recycle ships to get the debris with default options except for amount of time set to 24 hours
2) I eventually some of sent my Juggernauts also present at the battle site to the same coordinate to recycle, also specifying 24 hours, else default options
3) I noticed a short battle start, but did not immediately pay attention to it as I saw there where no enemies in the coordinate: Battle report: https://xcraft.net/battle/index.php?battle_id=ef0d23b765b103548d05e3f1e3f95250
4) I noticed slightly later that my other recycles was moving, and checked the log: https://prnt.sc/pfilg4
 
As you can see, I must have gotten extremely trigger-happy and attacked my own recycling ships!! Also - the other units that were still present at the defense point got into battle. 

In this case it did not cause a huge impact as the time lost and Vespene spent going between the recycling field and the locale defense point was low. It would have been very bad though if I had sent my ships on recycling mission from my colony instead and this happened...  

If you send an attack mission to nothing on coordinates, a battle will start anyway

Any units still at the coordinates will join the battle 

Your recyclers was not set with aggression on, and so they flee from the battle. Because a battle start

Recyclers without the option of aggression can be driven away with any fleet, even yours,which is not a bug.recyclers without the option of aggression can be driven away by any fleet, even their own, which is not a bugrecyclers without the option of aggression can be driven away by any fleet, even their own, which is not a bugrecyclers without the option of aggression can be driven away by any fleet, even their own, which is not a bugrecyclers without the option of aggression can be driven away by any fleet, even their own, which is not a bugrecyclers without the option of aggression can be driven away by any fleet, even their own, which is not a bugrecyclers without the option of aggression can be driven away by any fleet, even their own, which is not a bugrecyclers without the option of aggression can be driven away by any fleet, even their own, which is not a bug