为什么我的签名修订号在分离签名后增加2（在itext中）？

Having implemented a client-server signature webapp as explained in the B. Lowagie book :"Digital Sinatures for PDF document"(version : Signing a document on the server using a signature created on the client). I encounter this issue : when I sign a pdf document (with preexisting empty signature field),the signature is valid (in adobe reader or in itext ), the affected revision of this signature is 1 but the total revision number changes from 0 to 2 (preventing the signature to cover the whole document).(In adobe reader, the document has only one revision) Having implemented a client-server signature we