few patch ago we implemented the fact that :
1st situation :
a player A give a unit to player B
if player B die, player A get the unit back.
2nd situation : (that always been like that)
a player C give a unit to player D
if player C die, the unit die.
1st exploit (already know) :
C give unit to D, then D give unit to E
if C die, unit will not die.
2nd exploit (un-knowed i suppose) :
A give a transport to B,
B load unit into the transport,
if B die, A get the transport back + the unit in it.
FUN FACT :
A give transport to B
B load his commander in the transport
if A die, B need to drop before transport get killed or die too.