Image disappears from WYSIWYG editor in documents with special characters in name

If a document's name contains special characters (like German umlauts ä, ö, ü etc.) images do not work correctly in the WYSIWYG editor.

To reproduce:

• Edit a page witch such a name in the WYSIWYG editor (example: http://wiki.erlhagen.de/xwiki/bin/view/Sandkasten/Image+Upload+Pr%F6blem)
• Go to the end of the text and press ENTER to insert a new line of text.
• Click the icon "Insert/edit image"
• Choose one of the existing image files (or upload a new one and select it).
• Click "Insert"
• Then click Preview, or Save & View. The image is gone!

It works in the Wiki-style editor.