Good questions. Should have said more in my original email.
1. Exact behavior is that Emacs freezes for about a minute and displays (in bold) in the type of the word I'm over.
Thus, I was trying to edit a small a-list with dummy 0.000s in the range. Every third keystroke, emacs stopped to tell me that
my cursor was over 0.000::Double and I have to wait an indeterminate time (at least tens of seconds, sometimes a minute or more)
to get control back.
2. This is in Windows (8)
3. No the rest of the system does not freeze, thus allowing me to bring up the process monitor and kill emacs.
4. I can't identify a combination of keys that does this. It seems to be entirely random when I am moving the cursor around.
5. Turning off doc mode (etc.), which I first guessed might be the problem, does not help.