Just solved my problem !!!
Thanks to a tip in the now defunct Bagelturf website (available thru the Wayback Machine here: http://bit.ly/KzMBEv) the solution is simple and elegent:
Simply type the term in the search box at the top of the HUD. This will shorten the lenght of the list, allowing you to drag the keyword down and have the white highlight appear around the entire list.
Still curious if anyone has an issue with nested keywords being place at the root....
Bagelturf?! We got yer (un)lox right here:
As noted, keywording is still not fully matured in Aperture. There is no way to import nested keywords that are assigned to files. All attached keywords are imported at the root level.
My bad. I did search before posting, but obviously not well enough.
(I do think the newer Discussion search is not as good as before, but...)
Turns out this solution has been around since 2007: (OS 10.4.6 !!!!!)