ive had the same issue, after i did the extraction i went back to the home page and hit the reload paths and then under the gump tab everything still showed up. and there is a gump.mul file in the folder.
You are trying to extract new types of UO files. Since roughly version 7.0.60, these files have not worked well. Some file format has been changed at the game manufacturer. I recommend editing older versions of Uo, to 7.0.60.