Enabling xim causes mouse scroll to switch tabs

echo export GTK_IM_MODULE=xim >> ~/.xprofile 
startx

Open multiple tabs, then scroll horizontally. Expected behavior: stay in the same tab. Unexpected behavior: tab is switched.

Note that "scroll horizontally" might not work with a Shift+mouse scroll. This should be done via a laptop touchpad. In particular, xev, should give for RightScroll and LeftScroll the following

ButtonPress event, serial 32, synthetic NO, window 0x3600001,
    root 0x55b, subw 0x0, time 7734201, (689,572), root:(722,609),
    state 0x0, button 7, same_screen YES

ButtonRelease event, serial 32, synthetic NO, window 0x3600001,
    root 0x55b, subw 0x0, time 7734514, (689,572), root:(722,609),
    state 0x0, button 6, same_screen YES

You can also check input via screenkey -M