A hash of the file is sent to Xolox prior to being downloaded, which is a kind of a "fingerprint" of the file. Xolox checks that the file matches the hash after downloading to be absolutly sure the file is what has been expected. If you have been having frequent trouble with transmission errors, then the hash is less likely (but not gauranteed) to match the file you have actually downloaded. By turning off dropping bad segments, Xolox does not fix the ile as soon as itr realizes something is wrong. However, the file can still not match the hash after that as well.