aakk9999 - 6:20 pm on Sep 12, 2013 (gmt 0)
This is in fact a fairly common issue and we had a number of threads on this over past few years.
Some time ago Tedster suggested it could be because of internal anchors that may help the page they are on (rather than page the link points to [webmasterworld.com...] )
External links may also have the influence of home page ranking above internal page. Sometimes this is a problem if internal page is a better page for the visitor to land to, in other cases it may not be a problem as the home page may be a good choice anyway.
There were also cases where Google kept swapping home page with internal page in SERPs and the ranking fluctuated as each of these pages would rank in different position in SERPs.