If you try to drag from ROX Filer (2.1.4) a file with blanks in the name, to a panel entry, it is rejected by the application, it is rejected because the " " is converted to "%20". If we do this from xffm, it works. I don't know it the error is in ROX (KDE and xfe do not allow dragging to the panel), but it seems to be related to char encoding during the "transit" thru the panel - My Debian is using UTF-8.
Yes, rox seems to convert certain characters and Xfce does currently not support that. This is the same bug as 459. *** This bug has been marked as a duplicate of 459 ***