If you manually open the vaults using CryFS in terminal (cryfs yourencryptedfile.enc ~/mountpoint) there's an information that: This filesystem is for CryFS 0.9.7. It can be migrated to CryFS 0.9.8, but afterwards couldn't be opened anymore with older versions. Do you want to migrate it? Your choice [y/n]: If you migrate the filesystem then Plasma Vault will be able to open it without any problems. My proposed solution would be to automatically migrate all Vaults to 0.9.8 CryFS filesystem.
*** This bug has been marked as a duplicate of bug 389038 ***