I'm confused about organic search again

I have been blogging for about a year and it shows. I have learnt quite a lot but there is still a mountain of stuff that I don't know. What is confusing me at the moment is how blog posts appear in organic search engines and what that means for people following links to the blog.

When an organic search for a keyword term lists a post from the blog it seems to be entirely random whether the listing links to:

• the home page (which shows the newest post rather than the post that appeared in the search listing) which means that some visitors leave without actually finding the post that they found on the search engine
  
• all the posts which contain one of the labels from the post itself (Blogging; Business and so on)
• the post itself

The confusion arises because I use the same basic process whenever I make a post. I publish it with the appropriate labels and then I link the post to the same labels on Del.icio.us. That's it. If I was doing something radically different each time then perhaps it would be easier to understand. The BUT is that organic search engines are supposed to deliver relevant links irrespective of the workflow that created the content, and what could be more relevant than the original post?

It doesn't matter much at one level - I'm writing this, not searching it - at another level it is an indicator that organic search is behaving unpredictably and while that is the case, we don't honestly know if we are getting to see the most relevant returns to our queries.