sometimes when rebalance the SDK client stops working properly: ERROR Exception while rendering object of type [Common.Logging.Factory.AbstractLogger+FormatMessageCallbackFormattedMessage]

commit 700953b5c5323eaeb04d9d8a089d8c8d435ea0c9 from http://review.couchbase.org/#/c/50675/

from time to time in some tests when rebalance is started I see many errors like:

[977.98 INFO] (SDKD log:137) log4net:ERROR Exception while rendering object of type [Common.Logging.Factory.AbstractLogger+FormatMessageCallbackFormattedMessage]
[978.00 INFO] (SDKD log:137) System.NullReferenceException: Object reference not set to an instance of an object.
[978.00 INFO] (SDKD log:137) [Sdkd.Result|Warn] Unrecognized return code 512 
[978.01 INFO] (LineGobbler doFilter:115) +++ Following exception has internal ID: 1
[978.01 INFO] (SDKD log:137)  at Couchbase.Core.Buckets.CouchbaseRequestExecuter.<>c_DisplayClass49`1.<SendWithRetry>b_45(FormatMessageHandler m) in d:\couchbase_src\couchbase-net-client\Src\Couchbase\Core\Buckets\CouchbaseRequestExecuter.cs:line 391
at Common.Logging.Factory.AbstractLogger.FormatMessageCallbackFormattedMessage.ToString() in c:_oss\common-logging\src\Common.Logging.Portable\Logging\Factory\AbstractLogger.cs:line 75
at log4net.ObjectRenderer.DefaultRenderer.RenderObject(RendererMap rendererMap, Object obj, TextWriter writer)
at log4net.ObjectRenderer.RendererMap.FindAndRender(Object obj, TextWriter writer)
[978.02 INFO] (SDKD log:137) log4net:ERROR Exception while rendering object of type [Common.Logging.Factory.AbstractLogger+FormatMessageCallbackFormattedMessage]
[978.02 INFO] (SDKD log:137) System.NullReferenceException: Object reference not set to an instance of an object.
[978.03 INFO] (SDKD log:137) +++ Received exception of ID 0
[978.03 INFO] (SDKD log:137) log4net:ERROR Exception while rendering object of type [Common.Logging.Factory.AbstractLogger+FormatMessageCallbackFormattedMessage]
[978.03 INFO] (SDKD log:137) System.NullReferenceException: Object reference not set to an instance of an object.
[978.06 INFO] (SDKD log:137) +++ Received exception of ID 0
[978.07 INFO] (SDKD log:137) log4net:ERROR Exception while rendering object of type [Common.Logging.Factory.AbstractLogger+FormatMessageCallbackFormattedMessage]

http://sdk-testresults.couchbase.com.s3.amazonaws.com/SDK-SDK/CB-4.0.0-2029/ReAdd2-HYBRID/05-08-15/083827/57c74f5ada3ba8e0f049bab96c8a270c-MC.html

http://sdkbuilds.couchbase.com/job/win008-cbsdk-net-client2/325/consoleFull

it happens in different scenarios: rebelance out with/out master, swap rebalance, failover cases