Xev показывает
ButtonRelease event, serial 35, synthetic NO, window 0x2000001,
root 0x212, subw 0x0, time 289958499, (61,132), root:(932,563),
state 0x0, button 9, same_screen YES
ButtonPress event, serial 35, synthetic NO, window 0x2000001,
root 0x212, subw 0x0, time 289959023, (61,132), root:(932,563),
state 0x0, button 8, same_screen YES