WebSocket Endpoint's onClose not always called on close

When closing the browser, my Endpoint's onClose handler isn't always
called. I can recreate this by connecting to the Endpoint in 3-4
browser tabs in a single window, then closing the window. I see
onClose being triggered for 1-2 of the connections, but rarely for
all.

After the browser is closed, all of the Sessions that were created
return false for isOpen.

If I run a similar app in Undertow (1.1.0.Final) that uses a
WebSocketChannel directly, I don't see this behavior -
WebSocketChannel.onCloseMessage gets called for every connection,
which leads me to believe the issue is somewhere in the jsr
implementation.

Let me know if you need any more details, or want me to test anything
on my end.