The bug was closed but it is not fixed, as explained in last comments. The fix is not to be expected from a new version of timidity as it rather is a packaging bug.
As stated in https://www.freedesktop.org/wiki/Software/PulseAudio/Documentation/User/PerfectSetup/ (cited above by Gabriele Stilli), the timidity user should not be added to "audio" group. This is indeed what the timidity-daemon.postinst does at line 17, 44-51. So my understanding is that the packaging needs to be fixed. Side note : https://bugs.launchpad.net/ubuntu/+source/timidity/+bug/1793640 is the corresponding bug in Ubuntu.
