Mouse wheel behaves inconsistently wrt volume change in indicator applet and popup

[yoyoma2]

Description: Ubuntu 18.04.4 LTS (upgraded from 16.04 LTS)
Release: 18.04

indicator-applet-complete:
  Installed: 12.10.2+17.10.20170425-0ubuntu1

1) log in with flashback compiz or flashback metacity
2) Mouse wheel over volume indicator
= Volume is adjusted but popup volume display is missing

alternatively

1) log in with flashback compiz or flashback metacity
2) click on volume indicator
3) Mouse wheel over horizontal volume bar in menu below volume indicator
= Volume is adjusted in reverse direction and popup volume display is missing

Note:
Logging in with ubuntu instead of flashback does not have this problem

This issue is very similar to downstream bug in MATE desktop.

https://github.com/mate-desktop/mate-indicator-applet/issues/36