Couchbase 5.0.0: ERROR net.spy.memcached.protocol.binary.GetOperationImpl: Error: Auth failure

I upgraded to Couchbase version 5, which works great. Client side moxi authenticates well to a bucket. But later on if spymemcached tries to create an actual session I get the error:

ERROR net.spy.memcached.protocol.binary.GetOperationImpl: Error: Auth failure

The problem is described in this issue:

Does anyone have an idea what goes wrong?

Thanks!

Pieter