As per Filipe's comments:
One thing to note is, when the map function of a view fails with a document X, map results for other views of the same design document won't be computed for that same document X.
Only way to avoid this is by having the views in different design documents. This is a limitation inherited from Apache CouchDB, maybe we can get rid of it post 2.0.
This can be little confusing for the users as views appear to be independent of each other.
See http://www.couchbase.com/issues/browse/CBSE-238 for an example case.