Debian :: Sudo Results In Strange File Owner

I like the "Ubuntu" sudo philosophy and wanted to setup this sudo the same way on my Debian system. I was happy when I found that I just have to do the following:
-create a group 'admin'
-adduser christian admin
-visudo
-add the line: %admin ALL=(ALL) ALL

Then I tried sudo rm -rf / to check if sudo works. All worked fine. No, seriously, I can move around files that belong to the root and such, so sudo somehow works. But when creating new files with sudo, like e.g.
tar xzf myZippedTarball
these files belong to user 41034 and to the group users instead of root root:
drwxr-xr-x 7 41034 users 4096 2009-11-01 01:07 libsvm-2.9
Certainly, this is not the way I want to have. The user 41034 doesn't even show up in /etc/passwd...