Executive summary: use ctrl-alt-o instead of ctrl-o in crosh to save file in nano on remote host.
I complained, here: at hackernews.com that in crosh I could not use ctrl-o when ssh-ing to remote machine and editing a file with nano, because chromium maps ctrl-o to open new item, and it intercepts the key combination and it is not passed to crosh, and thus nano does not get the command to save the file. After more than a year of frustration, and frankly not using the cr-48, I was about to get rid of it. Then, thinking maybe they had fixed the bug, I tried again. Alas, ctrl-o still didn't pass to nano, but was intercepted. Almost by accident, I pressed ctrl-alt-o, and, O Wonder, Nano interpreted it as ctrl-o while chromium interpreted it as ctrl-alt-o, and let it through. Moral of the story: never give up.