[Cinnamon 4.0.9 - GWL] Bug - Browsers can get unpinned when closing Private/Incognito window

Browsers becomes unpinned from panel if I close a window in "Private"/"Incognito" mode while there is no regular window. It only happens when windows are not grouped ("Group windows by applications" unchecked); no problem when the option is enabled. Reproduced on real hardware on Manjaro Cinnamon with Firefox, Chromium and Opera. Also reproduced in a VM (Virtual Box) on Linux Mint 19.1 with Firefox and Chromium (didn't check Opera). CPU: Intel i5-6400 (4) @ 3.300GHz GPU: NVIDIA GeForce GTX 970 (using non-free drivers) --- Yes, the video said Feb 6, 2018. I meant 2019*. My bad. ---- Reported here: https://github.com/linuxmint/Cinnamon/issues/8377 ---- Music taken from: https://www.youtube.com/watch?v=hBlGaQXxCvA (C) Angéla et Gilles B.(Chispazito)