Can't hangup call made from Zulu soft phone

Using Zulu 13.0.49.8 and client 2.0.5 on Windows.

First I have to say Zulu looks really nice and very promising! Glad to see FreePBX UC capability growing.

I have an issue.
About 50% of the time when I make a call from the soft phone, I can’t hang up the call. I click on the red hangup bar, but the call just continues. When I click it, the red hangup bar toggles back to the green dial button, but the call stays active. Then clicking the green dial button again changes it back to the red hangup button and so on.

Is there any debug information I can provide?

My FPBX box is on a network that I connect my machine to via OpenVPN. The necessary Zulu ports are opened.

Not sure how that’s related, but I frequently get:
2016-12-20 17:54:43] ERROR[6873]: tcptls.c:397 tcptls_stream_close: SSL_shutdown() failed: 5
== WebSocket connection from ‘192.168.1.254:64969’ forcefully closed due to fatal write error

What version of asterisk?

Asterisk 11.22.0
Distro 10.13.66-11
High Availabilty

Ya you need to update your Asterisk. That is a bug in Asterisk

Update to what version?