Strange behavior while using gimp (and other software)

[alecive]

Hello, I am experiencing a strange behavior while opening/saving files with Gimp. I have a multi-monitor setup, and I have set the following bspc rules:

# xprop | grep WM_CLASS
bspc rule -a Firefox desktop=^5 focus=on
bspc rule -a Sublime_text desktop=^6 focus=on
bspc rule -a Franz desktop=^1 focus=on
bspc rule -a Meld monitor=HDMI1 state=fullscreen focus=on
bspc rule -a Gimp monitor=HDMI1 state=floating focus=on
bspc rule -a Gimp-2.8 monitor=HDMI1 state=floating focus=on
bspc rule -a Eog state=floating focus=on
bspc rule -a File-roller state=floating focus=on
bspc rule -a URxvt state=floating focus=on
bspc rule -a Pick-colour-picker state=floating focus=on

When I open Gimp, it correctly shows up on monitor HDMI1. But when I open the file dialog (e.g. ctrl+O), the file dialog always shows up in the other monitor. This happens even though its WM_CLASS is Gimp, and it should be then covered by the bspc rule that I set before.

Furthermore, If I want to move the window in the HDMI1 monitor, it stays below the original Gimp window that spawned it, making it unusable. See screenshot below for a better description of what I mean with below (not sure if it's the correct term).

[zwsyscall]

I'm having the same issue. Anything that can be done?