Thunderbird keeping its pinned icon separate

Hi. I’ve set my pinned icons on main panel no to be separated on execution. Unfortunately, Thunderbird does not respect this setting.
Fresh F39 install, I have no such problem on other KDE distros.
Can somebody relate to this?
Thanks in advance.

I have the same issue with Thunderbird in Fedora 40 Mate using cairo-dock if I add a starter for Thunderbird manually:

Seems to be a wrong identification of Thunderbird. Similar to my other problem:

I had no issue under my former Fedora 38 (and previous releases).