I have the same "problem".
My index was a "reasonable"
PR 4, as the most important internal pages.
Just few days agoo the index dropped to a
PR 1 and some internal pages went up to a
PR 5. the most part of the links from other sites (several) are to the index page, not to the internal ones.
It is a fact that my index page is more a presentation of the website, just few photos, a good text pretty well optimized (I hope) and links to few main internal pages and those pages work as web site map to reach all the site features. May be that this is the reason why the different stange pageranks?
Anyway for now my website (index) ranking on gg is the same than before and it is in the forst page for all the relevant keywords combination.
Do you think that I can sleep relaxed of may be that some bad surprise is coming soon?
The website is
www.artofvenice.com
Ciao
Alex