[support] Why would an upgrade to the Plus_1 module mess up some (javascript?) pull-down menus?

[Chris G]

I have been slowly working my way to finding which module update had
caused this problem, finally found it today, updating the Plus_1 module
from version 6.x-2.6 to version 6.x-2.7 breaks the pull down menus on
this site.

The working site is:-
    http://www.globaloptimists.org/

I have a copy, with Plus_1 updated to 6.x-2.7, at:-
    http://globaloptimists.isbd.net/

As you can see the menus at the top are permanently pulled down on the
updated site.

Can anyone suggest where I should be looking to see what is causing the
problem?  It's not urgent as I'm quite happy to leave Plus_1 at version
6.x-2.6 for the present.

-- 
Chris Green