Hi, Mike
Thanks a lot for responding!
When it happened, all id values are affected. I built a test index with one shard and 21,000 sample docs, on which the problem can be reproduced. The index files can be downloaded from
https://drive.google.com/file/d/0B6UVCJccYns8VVpwYURTbTlSMGM/view?usp=sharing