The one exception to this din is that after the master of the eved dies, the eved is still bound to work for master’s sons. It seems that this din of “kam tachtav” is not a halacha in yerusha or kinyanim, as that would undermine the Ralbag’s chiddush, but rather means that so long as the owner has a son, it is as if the owner himself is still alive – the son is not a new owner, but an extension of his father’s ba’alus (see Koveitz Shiurim II:12).
Minchas Chinuch asks: the din is that a father cannot pass on b’yerusha rights he has to his ketana daughter. For example, a father has a right to the earnings of his daughter. If the father dies, this right does not pass through inheritance to his sons. If so, based on the chiddush of the Ralbag, a father should not be able to sell his daughter either. Clearly this is not the case, so your homework is to come up with a chiluk between the two halachos.