Hmmm.....weird. I have this problem too. Why does it happen? The number of backlinks to my internal page is very little, most of them goes to the frontpage.
You might want to also check your internal links. Internal link building is also very important aspect in your site to focus on. If you have pages within your site pointing to that page than you may be spreading the page rank to that page. Why dont you point more links back to your home page from the high pr page this will than help to increase your hom pages page rank
Exactely, and even it dosn`t mean it is important from the other. I have some PR4,5 pages and my main site have PR3 In Google webmasters tools, it told me that my highest page is the main page! It`s about the value not the number anymore.
This happened to me once. An internal page had higher PR than the home page. It was the only internal page with the higher PR, and it had exactly one difference from the other internal pages with lower PR — the higher PR internal page had some good-quality inbound links. I had secured those links via an email campaign targeted towards that specific inner page.