documentation for XMonad.Actions.UpdateFocus says it "Updates the focus
on mouse move in unfocused windows." However, for me (using Ubuntu
16.04, xmonad installed from Ubuntu repository), it doesn't seem to have
I'd have to review xmonad's setup code to be certain, but I think the startupHook no longer works. Instead, the mask changes it makes need to be exported and applied to the rootMask and clientMask fields of the XConfig.
File a bug on the xmonad-contrib issue tracker, please, referencing this message from the list archives.