MDT should update PFID information to OST objects after layout swap, split, and merge. However, a protocol should be defined to make this correct. Fanyong proposed to use synchronous OUT setxattr. However, I tend to think it would be better to use llog as SETATTR and DESTROY RPC.
This problem has been existing for really long time since Lustre 2.4. LFSCK could fix this problem but it's better to have a mechanism to solve this kind of problem because there will be more and more similar problems.