PDF Explorer try to update the metatags in both places, database and PDF file itself. Do not forget that you have to rescan the folder where that file is using the direct scan mode, DiskTree, in the other user computer with its local PDFE copy.
You can easily check if the files had been updated or not. Just open them in Acrobat and check the metadata fields.
Are you updating the file in a shared folder with UNC path, folder mapped to drive letter, local path, ... ?
If even using local path the file is not updated, please send me one of these file so I can check by myself if some incompatibility exist.