What causes redisplay?

[Lennart Borgman]

In mumamo I have to temporarily narrow the buffer when turning on a
major mode in chunk. However under some circumstances the buffer is
redisplayed during this short temporarily narrowing and I wonder why.
It looks like a bug somewhere in Emacs to me, but I am not sure.

The redisplay happens if I add this

   (add-hook 'python-mode-hook 'turn-on-eldoc-mode)

This runs a subprocess with python and I guess it has something to do with this.

I am seeing this with an Emacs compiled from sources checked out 2010-01-26.

PS: I can work around this by temporarily setting inhibit-redisplay to
t during the narrowing, but I am not sure what trouble that may cause.