causal_reads=global returns an unexpected OK packet

The OK packet returned by the MASTER_GTID_WAIT() call that causal_reads executes is not always removed.

This was reported along with a network trace and from it can be seen that the same query sometimes returns an OK packet with the more results follow flag set. Theoretically this could be a bug in the server but the simplest explanation is that under some conditions MaxScale fails to properly process the result.

I have yet to reproduce this with a similar setup and a script that repeatedly executes a query that returns a known row that has replicated to the server.