WindowsXP only recognizes 8.1 names on thumbdrive

I have a desktop system running XPpro with all updates. Recently this computer stopped reading longfilenames on thumbdrives correctly. Before it read them correctly. Now it truncates the filenames to 8.1. It also truncates the name of files I save to the drives. I tried saving some files then took the drive to another computer and only those files I saved from the afflicted computer showed up in 8.1 filename format. I have tried multiple thumbdrives, same thing. These same thumbdrives work normally on any other computer I put them in.