I don't know what the reason can be. It's very strange.
The only thing I can think of is the auto save feature in
WordPress. By default, it auto saves every 60 seconds. It does it
in the background so you don't even "feel" it.
But the problem you are describing should not be caused by
the auto save feature which for some folks has acted a little strange
with different symptoms, not the one you are stating.
In any case, not knowing what the reason is, the next best thing
is a shot in the dark.
If it works, OK it works. If it doesn't, then a General may have the
right and straightforward solution to your problem.
A shot in the dark
Using your FTP, make a temp directory on your hard disk,
anywhere, but remember where.
Copy wp-config.php file from the root directory of your blog over
to your PC hard disk in your just created temp.
Save it by making a copy some place where you can access it easily.
Remember where you save it. This copy is for the time when something
goes wrong and you need to bring the server side wp-config.php back
to the original configuration.
Now open the temp directory copy of wp-config.php in MS notepad.
Go through the
auto save exercise here.
After you make the change, replace your wp-config.php on your
server.
If it works and solves your problem and I have no idea why it would work,
you are in business.
If not, then you can always replace your wp-config.php on your
server with the saved original file.
Like I said in the beginning, it's a shot in the dark. It cannot be the
real solution. I hope generals and more experienced folks would have the
straightforward solution.