i can't replicate this issue on my laptop which is a largely identical setup with either geany or geany-gtk3. these packages are the same on either laptop or desktop.
glib2 2.52.3-1 gnome-shell 3.24.3-1 gtk2 2.24.31-1 gtk3 3.22.19-2 wayland 1.14.0-1 wayland-protocols 1.10-1
On desktop both geany and geany-gtk3 exhibit the reported behavior. pls see geany-wayland-debug from desktop machine: https://pastebin.com/70p3UmWw thanks