I have since figured out what is causing the problem, but not an effective solution.
I compared the HTML code of my new post (WP2.6 generated) with that of an older (WP2.5.1 generated) post. I discovered that with 2.5.1 the code "float: left;" and "float: right;" appeared in the HTML view of the post. These snippets of code are not appearing for the pictures that I placed and formatted with WP 2.6. After I manually added this bit of code for each picture, all was good.
Now the question becomes: "Why does WP2.6 no longer automatically place this bit of code into the HTML when working with pictures?"
Does it expect that it resides elsewhere (maybe in the alignleft/alignright functions in a style sheet somewhere?
I apologize if I've butchered some of the HTML details, I'm new to HTML coding.