Just take a look at the source, it doesn't seem like the remainder parameter is ever used.
Reproduction is as simple as
String remainderAddress = ...; List<String> transfers = iotaAPI.prepareTransfers(seed, 2, transfers, remainderAddress, inputs); for(String trytes : transfers) System.out.println(remainderAddress.equals(new Transaction(trytes).getAddress());
this snippet will never return true as the remainderAddress is always generated!