URL field in image browser begins with 'http%3A...

hi,
I need absolute pathes for the images placed in the editor-textarea. So my image-files begins with 'http://...'. But after selecting an image in the image browser window, this window closes and in the ckeditor image browse window the field URL is set with a encoded filename (http%3A...) which is not recognized in the window to continue.
How can I fix this e.g. with a decodeURI or a replace('%3A',':')... Trials in plugin filebrowser (browseServer, updateTargetElement) where not successful.
Thank you for your help.