When editing the description for a job, utf-8 characters get encoded twice resulting in broken characters (or rather 2 byte chars get encoded to 4 bytes).
When editing the appropriate config.xml file manually, the text comes through ok, so this probably an error when processing the input text that is passed as url encoded form values.
I couldn't reproduce this with hudson running on Windows, so it is probably a environment dependency or is affected by locale settings, but I couldn't get it right in Linux.