The fixed library will be delivered upon the next public release of LS.
No patch for LS 5.x has been planned at the moment;
so, the case should be the next alpha release of LS 6.0
(where the included .NET Client library will be still compatible with Server 5.x).
This should happen within a few months, but no date has been scheduled yet.

If you are a customer, with an active support & maintenance contract, then you can receive a library patch in short time, by requesting it to support@lightstreamer.com