At least both "Recently build" streams feed and dashboard suffer from this problem.

When you first load the dashboard all umlaut names are fine, say "Emmi Mämmi" is displayed correctly. But when you wait for background update then when it happens the name changes to "Emmi M�mmi" (on my firefox the 'ä', umlaut-a is displayed as question mark). If you hover over the name the full name is shown correctly in the popup.

Recently build feed does not work at all if the users have umlauts in their names. FireFox's error console gives invalid XML errors from response (even though it should be UTF-8).