Encryption of a new file added to protected folder

An authorized user is adding files to a protected folder but the added files do not encrypt automatically. I know this because, when I check the folder status, it shows that the number of files un-encrypted matches the number of files added. A re-encrypt fo the folder does encrypt the new files. From the documentation I've read, adding files to a protected folder should encrypt them automatically. Have I missed something when establishing the protected folder?