@PaveThem, I doubt was the case. I've been using nautilus as an alternative to pcmanfm due to this issue, and there was no problem with it even with gnome libraries prior to 3.30. Furthermore, I tested both alternatives available in Arch Linux for pcmanfm, pcmanfm (based on GTK2) and pcmanfm-gtk3 (Based on GTK3 ), and both alternatives have this issue, at least from August until today. So I guess is mostly related to pcmanfm.
Same here in Arch linux pcmanfm 1.3.0-1 kernel 4.14.56-1-lts x86_64 openbox based environment