I've had this experience with 2.x and as I recall, on machine B where the file was already open with unsaved changes, I was prompted to merge changes after Dropbox updated the file on disk. Without recalling the details, I was pretty impressed.
Ah okay. Did not know there was a merge function!
We use a source code repo to handle this. Not perfect but better than losing a password.
For example say on PC-A I make a change and save it. On PC-B I have the old database still opened and loaded in KeePass. What happens if I then save in PC-B without opening the database up? That means I just lost the one password?