Some ekstra info. I have installed the newest version of the widget and it seemed to work great. However, since I need two of these (see my post above) and the Fuji one for some reason can only be used once, I have deactivated the widget and kept the one I have found elsewhere. What that caused was this (at the bottom of the page):
Warning: call_user_func_array() expects parameter 1 to be a valid callback, first array member is not a valid class name or object in /home/content/79/9731479/html/wordpress/wp-includes/plugin.php on line 403
(Well, at the time I had no idea what caused this line, but as soon as I put WordPress into debug mode I was able to locate the culprit quickly :).
Replacing the new widget with the old version seems to have fixed the problem (the warning line is gone).