I have an issue with WP to Twitter plugin and my YOURLS-installation. If I manually create a shortlink from a page with umlauts (ä, ü, ö) in the title, everything looks fine in YOURLS Admin Interface. But if WP to Twitter shortens my links automatically, the umlauts seem to be encoded the wrong way in my YOURLS-backend.
I found a somewhat similar issue here: http://code.google.com/p/yourls/issues/detail?id=136
Maybe it can help to solve this bug?