How is libinput's ScrollMethod supposed to work?

I'm trying to configure libinput according to the official documentation: http://manpages.ubuntu.com/manpages/bionic/man4/libinput.4.html. However, when I set the ScrollMethod property to button with xinput, it does not enable middle button scrolling system-wide. Instead, it blocks the middle button scrolling even in the browsers where it worked before.

How to reproduce this behavior:

1. Find out the mouse id (11 in my case).

$ xinput | grep -i mouse
⎜   ↳ VirtualBox mouse integration              id=9    [slave  pointer  (2)]
⎜   ↳ ImExPS/2 Generic Explorer Mouse           id=11   [slave  pointer  (2)]

2. Find out the option number (275):

$ xinput list-props 11 | grep -i scroll
    libinput Natural Scrolling Enabled (266):   0
    libinput Natural Scrolling Enabled Default (267):   0
    libinput Scroll Methods Available (274):    0, 0, 1
    libinput Scroll Method Enabled (275):   0, 0, 0
    libinput Scroll Method Enabled Default (276):   0, 0, 0
    libinput Button Scrolling Button (277): 2
    libinput Button Scrolling Button Default (278): 2
    libinput Horizontal Scroll Enabled (273):   1

3. Set the option 275:

$ xinput set-int-prop 11 275 8 0 0 1

4. Make sure it is set:

$ xinput list-props 11 | grep -i scroll
    libinput Natural Scrolling Enabled (266):   0
    libinput Natural Scrolling Enabled Default (267):   0
    libinput Scroll Methods Available (274):    0, 0, 1
    libinput Scroll Method Enabled (275):   0, 0, 1
    libinput Scroll Method Enabled Default (276):   0, 0, 0
    libinput Button Scrolling Button (277): 2
    libinput Button Scrolling Button Default (278): 2
    libinput Horizontal Scroll Enabled (273):   1

5. Observe mouse button scrolling blocked everywhere.

So, what am I doing wrong? The answer "don't bother, it's bugged" will be accepted too.