A few of my users recently complained that they don't like su.pr, so I tried to switch to bitly and tinyurl, but there was no change.
If I switch the setting to none, the url shortening (su.pr) disappears when I click on the twitter share button, but when I switch it back to any of the other settings (digg, bitly, or tinyurl), it reverts to sup.pr. In other words, the only two options are su.pr and none.
I tried clearing my object cache, and that didn't work - I'm also able to make all sorts of other changes (which share buttons appear, their order, etc...). Only this doesn't work.