Icon only shown when program run as root

[Betterbird]

While integrating libayatana-appindicator into Betterbird, we noticed that the icon was only shown when the program was run as root under newer versions of Mint/Xfce, see table here:

Betterbird/thunderbird-patches#20 (comment)

We got a tip how to solve this issue from a KDE developer. In the end, we needed to patch the library removing one line, see here:
https://github.com/Betterbird/thunderbird-patches/blob/be991b0b382c12a0b8199bb26d79d3f667805d32/102/features/12-feature-linux-systray-no-root.patch#L20

This is reproducible with the test program here:
https://github.com/AyatanaIndicators/libayatana-appindicator/tree/master/example