Just realized that Google Shared Items are sorted with the date of the post and not the date on which you have shared the item. I think it should probably be sorted by the date of sharing than the date of the original post, after all its your shared items and you should have control over sequence of sharing.
Most of the times I skip a log of blogs and only choose a particular few, but when there is time I tend to catch up all what i skipped through. If a share something which actually is a post from an old date, the shared item list shows it down the list after the items which I shared earlier.
This actually caused a problem with TwitterFeed which would only select based on the last updated item (probably with date) and do not update the items which I share from previous dates.