Sometimes you get a pulldown list on wiki pages (e.g
theme akwa or bluegreen) on right top called structeres
with a list to wich structures a wiki page belongs. You
get this only if a wikipage belongs to more than 1
structure. If you look closer to that feature you mention
that this pulldown list is not shown always. For the same
page (into 2 or 3 structures) I sometimes see that list
and sometimes not. It seems that it depends at least
from where you come. It never shows up if you go to a
page from a toc. But even If you came to the page from
a wiki link it is not always there.
I looked into the tpl-File (templates/tiki-show_page.tpl)
there is an if sequence to show the pull-down menu only
if $structures >1, it seems that $structures is sometimes
undefined for a page and sometimes not.
In my opinion this list should be visible always if a page
is in one or more structures, at least if the page is in
more than one structure. If you tell me why $structure
is sometimes empty and sometimes not, i can fix the
template myself to show the pull-down list if needed.