[Bug 39320] New: Unrest doesn't exit properly (hangs on exit) with built-in Xaudio2

https://bugs.winehq.org/show_bug.cgi?id=39320

Bug ID: 39320
           Summary: Unrest doesn't exit properly (hangs on exit) with
                    built-in Xaudio2
           Product: Wine
           Version: 1.7.51
          Hardware: x86
               URL: http://store.steampowered.com/app/292400
                OS: Linux
            Status: NEW
          Keywords: download
          Severity: normal
          Priority: P2
         Component: xaudio2
          Assignee: [e-mail]
          Reporter: [e-mail]
                CC: [e-mail]
      Distribution: ---

The game remains in the process list after exiting the game.
'winetricks xact_jun2010' is a workaround (the game loads xaudio2_7.dll).
Plain terminal output doesn't show anything related.

Can be reproduced with Unrest demo on Steam.

The same problem occurs in System Shock:Enhanced Edition (released a few days
ago on gog.com). After pressing alt-x to quit the game, the game freezes.

FWIW, both games quit properly with built-in xaudio previously, this was the
commit which changed the behaviour:

commit a4fd0a7080f7ad32126c864389ab05d91b2f25fe
Author: Andrew Eikum 
Date:   Thu Aug 27 09:31:12 2015 -0500

xaudio2: Implement the audio mixing thread.

wine-1.7.51-201-g60d1d6f
Fedora 22 32-bit
Alsa 1.0.29 (pulseaudio is not running)
Openal-soft 1.16.0

~/.alsoftrc contains:
drivers = alsa