FVWM: [FVWM2] Since update: stalonetray leaves FvwmButtons

After more than a year, I did a system update of an Arch Linux
installation. Since that update, stalonetray starts popping out of
`FvwmButtons` upon start of X. You can find the original configuration,
which worked until the update, in my GitHub repo [hiwiwi][1].

What happens now: While starting X, I see stalonetray swallowed in
`FvwmButtons`. Stalonetray has three icons in it. Then, after a fraction
of a second, stalonetray pops out. And it pops out despite there being
no change to the icons.

*Could this be due to a change in Fvwm2 or stalonetray over the past
year?*

I have tried cleaning up and modifying `.stalonetrayrc`, to no avail:

    background "gray35"
    geometry 2x2 # seems that resizing later causes icons to disappear
    icon_size 48
    max_geometry 2x2
    kludges fix_window_pos,force_icons_size,use_icons_hints
    no_shrink true
    skip_taskbar true
    sticky true
    window_type normal

[1]: https://github.com/feklee/hiwiwi