Signature verification fails after allocation is transferred

[lpoli]

A writemarker is chained with previous writemarker. The writemarker that is responded by blobber before creating new writemarker by client, should be verified by the client, otherwise blobber can modify the content. The verification method is signature verification. It uses allocation owner's public key to verify the signature but when the allocation is transferred to new owner, the public key of current owner is no more relevant to verify the signature, hence fails.