when pacman downloads a db archive it extracts and removes (or extracts in a way that doesn't preserve). For clarity I'm talking like core.db.tar.gz. This is ok with default pacman setup because somehow pacman has another timestamp (or something) to check. This doesn't work if you change the download manager. I switched to wget because I need download throttling but now it will download all these files whether an update is available or not. Preserving the files would allow the timestamp to be checked on the remote.