Checkpoint information is not persisted in _local/vbstate document leading to loss of all checkpoint information after restart.

All checkpoint information is lost after restart:
1)Insert 100k items in default bucket.
2)Use couchstore API couchstore_open_local_document to get the vbstate json from a vbucket and read the checkpoint id. It is zero.
3)query stats for checkpoint using cbstats, it is different example:6
4)restart restart gracefully using restart command line command
5)use couchstore API to read the checkpoint information again, it is zero.
6)use cbstats to query for checkpoint information. this time it shows zero.
7)All checkpoint information is lost after restart.