When the persistent chat is minimized to the bottom of your window, as mentioned in T15626,
the chat bar still has an invisible square area that does nothing if you click it by mistake:
{F195}
That area was reserved for the Settings Icon, that appears only if you de-minimize the chat.
The Settings Icon was toggled incorrectly from CSS. It was just hiding the Font Awesome icon,
(.fa-gear), instead of hiding its clickable container.
After this change, chat can be de-minimized even if you click in that specific evil spot.
Original credit to @roberto.urbani for the original troubleshooting and original patch.
Follow-up from: D25428
Closes T15626