reduce error causes incomplete index

1. 1M items bucket
2. create good map function
3. create bad reduce function that fails (in our case it failed due to result size limit, but I don't think it's relevant)
4. save
5. indexing starts
6. indexing stops with error

Now we have something indexed, something not, because first reduce error aborts couch_view_index_builder process.

So far so good.

Now

1. fix reduce function
2. save
3. indexing starts
4. indexing stops

Now we have no diagnostic messages and everything seems OK.
Yet it is not so.
Some documents not make it into the index.
Query group=false&key="key1" returns less documents by key than there are in this bucket (in our case there were 2 documents, query returns only 1).

View map function update (added comment line) forces total index update, that helped and missing documents appeared in search API reply.