Windoz 7: ES 1.3.2: added some 6 million documents distributed over two index instances.
Decided to "bookmark" that collection by copying it to another directory in case something crashed going forward.
Copied the clone back to the index directory. On booting and looking at it from the Elastic HQ viewer, I could see that it recorded the size of one of the index, but showed 0 documents in it. The other (smaller) index still showed all its documents and proper size.