[GAMEPLAY] Sion's passive rewarding gold on last hit

Was spectating a preview ranked game with Sion vs Cassiopeia top. Sion died to a jungler gank, awarding her 150g (her jungler, Hecarim, got the 300g from the kill).

She kited his passive and killed him with a Twin Fangs (E), and she was awarded another 274g along with another 30g in a separate increment.

After reviewing more footage, it would seem that this bug is inconsistent, as later deaths did not have him awarding more gold upon expiration of his passive.