Hi,
the auto-recall when there is no more debris seem to not work under certain circumstances.
http://prntscr.com/lnvqtgHow it happened to me:
Send fleet to coordinates
Battle occurs -> finishes with draw
Send only 1 unit away (to the same coords) and instantly recalled to get a battle happen again to finish the pirate
Recycled all that was there
Units don't come back after the recycling was done (the last saved position was still the planet where I send from because I did not send all units away)
I need to recall the units manually in this case.
Probably the sending and recalling of a unit causes this.