This happened once so far, usually the failure happens earlier (CONTROLLER-1679).
This behavior is expected to change after the fix [0] goes in, we will probably reuse this Bug if the failure does not happen after that.

The suite calls write-transactions on a member, then isolates the member, then waits some time (60 second right now) expecting no failure, and then some time (20 s) expecting a failure.

This failure (or any other response) did not happen [1] when the target module-based shard has leader on the same member. Tell-based protocol, simple (as in not chained) transactions. In kkaraf.log [2] between 13:46:27,686 and 13:50:38,617 I see usual isolation-related messages only.

[0] https://git.opendaylight.org/gerrit/57074
[1] https://logs.opendaylight.org/releng/jenkins092/controller-csit-3node-clustering-only-carbon/693/archives/log.html.gz#s1-s32-t3-k2-k17-k1-k1
[2] https://logs.opendaylight.org/releng/jenkins092/controller-csit-3node-clustering-only-carbon/693/archives/odl2_karaf.log.gz