Two Questions Regarding Hash/Force Re-check and File Extension

[x0pht]

EDIT: Please ignore the first question, as I've figured out how hash check works with a few more tests after I got home.

Hopefully someone's able to shed some light on these.

1. What kind of hash does "Force Re-check" actually check?

I thought it checked the hash of every piece or file, and compared them with the hash values stored in the torrent file. but I did a little test earlier today.

a. deleted a torrent file from the utorrent seeding list

b. intentionally edited a text file in that torrent file, and made sure the checksum was different than the original

c. re-downloaded the torrent file, opened it in utorrent, pointed it to the right directory, and did a re-check

d. utorrent didn't find anything wrong with that text file, and moved the torrent to seeding right away after it finished the re-checking

so why's that?

2. Why does utorrent append .1 to some filenames with .!ut? (e.g. xxxxx.!ut.1)

I believe this happens when the individual file is finished downloading all the pieces, but i need more tests to be sure. What I'm sure is, it has nothing to do with the status of the torrent itself, i found it in both downloading and seeded torrents. So what happens is, if you stop and restart the torrent when .1 presents in some filenames, utorrent will for sure report "file missing". My best guess is that utorrent thinks there's a duplicate filename in the same directory, so it's unable to remove the extension .!ut after it finishes downloading the file.

but is it really the reason?