Not sure this qualifies as a bug, but:
use turn against, or any card that takes a creature for a turn. When it’s returned to your enemy’s control, they regain the creatures’ “enter battlefield” ability. Personally, I think one of two things should happen.
No effect, since it isn’t entering the battlefield.
The effect should happen both when you take it, to your creatures, and when it returns, to your enemy’s creatures.
Reported many times over months and months. Devs haven’t acknowledged this at all still, so just assume you’ll always give back a free EtB effect every time you use a borrow spell.
Is this fixed in any way? When the AI stole my Pia and Kiran Nalaar with Act of Treason, it returned to my side at the end of combat, but upon entering my side the card didn’t spawn four new thopter tokens. So it seems like it is fixed, but it wasn’t mentioned in the latest bug fix update.