[Collections] Collection creation succeeds but returns "unexpected server error, request logged"

Steps to Reproduce:
1. Create a 2 node cluster .137, .138
2. Load travel-sample bucket
3. Lose connection to memcached on .138 (stop memcached on .138)
4. Try creating a collection "some_collection",  making a rest call to .138

curl -X POST -v -u Administrator:password http://172.23.120.138:8091/pools/default/buckets/travel-sample/scopes/_default/collections/ -d name="some_collection"

works fine and returns 200 status with response:

{"uid":"2"}

5. Try creating one more collection "some_collection2"

curl -X POST -v -u Administrator:password http://172.23.120.138:8091/pools/default/buckets/travel-sample/scopes/_default/collections/ -d name="some_collection2"

returns:

["Unexpected server error, request logged."]

But checking on UI, the collection appears to be actually created (and will remain so even after failover and removal of .138 node)