wmctrl not moving some applications to different AwesomeWM workspaces

[ghost]

(copied from awesomeWM/awesome#2192 )

Output of awesome --version:
awesome v4.0 (Harder, Better, Faster, Stronger)
• Compiled against Lua 5.1.5 (running with Lua 5.1)
• D-Bus support: ✔
• execinfo support: ✔
• RandR 1.5 support: ✘
• LGI version: 0.9.1

How to reproduce the issue:
in the file ~/.config/awesome/rc.lua we have the last line with:
awful.util.spawn_with_shell("bash ~/.config/awesome/startupitems.sh")

in the file ~/.config/awesome/startupitems.sh we have stuff like:
conky -q &
sleep 2
wmctrl -r "conky" -t 8 &
sleep 2
mate-volume-control
sleep 2
wmctrl -r "mate-volume-control" -t 8
sleep 2

Actual result:

in the case above, conky window (i have it configured to be displayed in a window) get moved to workspace 9 (it’s the “8” there, workspaces 1 to 9 are 0 to 8 from wmctrl), and mate-volume-control doesn’t (from my bash script, i think gnote, chromium and caja windows also doesn’t get moved as well)

Expected result:
get (at least) mate-volume-control window moved to workspace 9 as well as conky window got

(note: i don’t know if it’s a specific wmctrl bug, a wmctrl bug related to AwesomeWM, or some misuse from me, and i neither know how to verify it and try alternative approaches - the fact is that i really consider wmctrl as an essential tool for AwesomeWM, specially when it is starting up )