[Plugin: WP to Twitter] Uses su.pr instead of remote yourls

I have a problem to use the yourls shortener (installed on a remote server) – possible since the update to 2.2.10, but not sure if not earlier. Instead of yourls it uses su.pr.
Yourls has worked before and I have not changed anything in the settings. The yourls installation is functional (also via the API from other plugins). Re-entering the yourls information didn’t not solve the problem, all settings seem to be correct.