Couchbase client returning wrong documents

Occassionally couchbase Get requests called via the .Net client return a completely different document to the one requested. This applies both to requests for single documents and multiple documents.

This behaviour has been validated by logging the key that was requested and comparing it to the response from the Couchbase client.

When this error occurs, it often affects several requests at the same time. It appears that simultaneous requests sometimes get mixed up, so that the document returned for one request was actually requested in another request that was made around the same time.

Another (possibly related) error which occurs is IndexOutOfRange exception which occasionally is thrown by the Couchbase client when requesting a key. Subsequent requests for exactly the same key usually work as expected.

These errors occur in a production environment with several web clients which use couchbase for logging events, sessions etc. They occur relatively seldom (several times per day) compared to the total number of requests (many thousand).

Examples:
Requested key 1: "systemAccount_widgets"
Response received at 2015-05-12 11:08:51,069
Document returned: "user_821eb769-f75e-4a29-aae2-95be1c005a74"

Requested key 2: "systemAccount_mytv"
Response received at 2015-05-12 11:08:53,128 - two seconds later
Document returned: "systemAccount_widgets" (i.e. document requested in earlier request!)