Guake (GTK3) started switching tabs on mouse scroll within terminal -- what causes this, where can this be (un)configured?

I use the [quake drop-down terminal](http://guake-project.org/) a lot. Recently, it started to switch between tabs when I use my mouse wheel anywhere in a terminal. Usually, I use the mouse wheel to scroll within the terminal, and _not_ to switch terminal tabs. Now the behaviour ist, that it does both: It passes a scroll event to the currently opened terminal tab, and switches to the next tab, and so on, until I stop scrolling. What might have caused this, and where can it be switched off; where is the corresponding configuration switch? I am not sure if this is a guake issue at all or some GTK3-"magic" which was silently imposed upon me with some upgrade. In the settings of guake (Right click -> "Preferences"), I don't see that I have mouse scroll assigned to any action, and especially under "Keyboard shortcuts", "Go to previos tab" and "Go to next tab" are assigned to `+ and +`, respectively. I am using guake version 3.9.1.dev0 (according to guake --version) from [Arch Linux](https://archlinux.org/packages/community/any/guake/)) . I am not using gnome, but I am using xfwm4 as window manager, without a desktop manager, and lightdm as session manager. I do start up everything I want to have ready at Xorg startup via ~/.xinitrc. I have already reported an issue upstream: [Here](https://github.com/Guake/guake/issues/2142) . Regards!