Ctrl-S doesn't work in rtorrent when accessed via screen. Can't start torrents

I run rtorrent remotely on a seedbox. When I log in with a web interface I'm able to start torrents, and when torrent files get dropped into my watched folder that works too. However, when I try to start them by SSHing in to my seedbox and -r resuming the screen session that contains my instance of rtorrent, I can't seem to use the Ctrl+S keyboard shortcut to start torrents. I can stop and delete them with the Ctrl+D shortcut, and as far as I can tell all the other keyboard shortcuts work. I've tried this from the Terminal app in OSX and from Cygwin on Windows. Thanks for your insight!