Comment by btdmaster

This is true, but there is a subtle point that key K1 used for the classical algorithm must be statistically independent of key K2.

If they're not, you could end up where second algorithm is correlated with the first in some way and they cancel each other out. (Toy example: suppose K1 == K2 and the algorithms are OneTimePad and InvOneTimePad, they'd just cancel out to give the null encryption algorithm. More realistically, if I cryptographically break K2 from the outer encryption and K1 came from the same seed it might be easier to find.)