I have noticed this problem. Let's say when I first see a question, it is in version $A$. It is badly formatted, so I click edit. However, it takes a long time for me to edit. Before I finish, someone click edit and submit a version $B$. However, at that moment, I do not know about it, so I submit my version $C$.
The end result is that I am not doing the edit that I intend. I intend to edit version $A$, not version $B$. I think this is analogous to race condition in a multi-process system (each user is analogous to a process). Is this a bug?
EDIT: This happens when I am reviewing first posts. Also, I have unstable internet connection. After I finish editing, is it possible to have an option to show the diff (like in Wikipedia)?