An example of this is in the names of some of my characters. This usually happens with secondary and transient characters as I am not as focused on them as I am the main characters. For instance, in my recent read through of version 2.0 of my novel, I noticed that I had switched the names of two secondary characters on more than one occasion. Liam became Finn and vice versa throughout chapters one through three. Several other ancillary characters seem to have simply changed names all together as I progressed onward from the Prologue. It seems that only Darby has remained constant over time.
The basic plot of version 2.0 has remained the same since it's inception five or so years ago. However, judging by my notes, it would seem that the details of how I intend to get through the beginning, middle, and end varied in scope and complexity based on the wiles of my imagination at the time. I started with my main character leaping off a cliff in chapter one (not to his death, but rather for dramatic affect) to an angry trot down a hallway in chapter two. I also find myself repeating plot elements in different chapters or even within the same chapter and not always with the same directional intent.
Even my setting has changed from the prologue to where I am now, though I put that more down to the "fleshing out" of the entire story. It is evolutionary in nature, really. A great deal of what I have described is due to my efforts to expand my world and the characters therein. I progress along with the story with one path in mind when my imagination sparks with a new idea that would add substance to the plot or at least bears exploring. The last of these was a new concept for chapter one that would add tension and not require too much rewrite in the other chapters.
Of course, we can't exclude out my woeful memory from this process. The biggest problem is that I do not sit for hours on end every day working on my story, but rather in stolen moments here and there throughout my week. Part of this is due to my own lackadaisical nature and the other is my day walker life (e.g. - the day job). This means that, as I pick up and leave off at random intervals, I lose track of the threads I was weaving. I am always thinking about the novel and a few other projects in the works, which is what leads to shiny new plot items and character idioms. Thus, when I go back to the story with the new gadgets and what not, I nearly begin anew.
What I am left with in the end is something akin to a diagram of the evolutionary tree of the Macaque monkey. A common thread leading from pre-history to present with branches that split from the main story only to end in extinction. Some my progress for some time before spiraling into oblivion, but such is the nature of things.
Some would argue that this is no way to go about things. Outlines, they cry! Rigid adherence to a pre-planned plot line is the only way to keep yourself on track, Focus! Dedicated time. Protected time. These things that you must do to maintain your continuity and sanity.
But then...where's the fun in that?