[ESS] How to re-identify chunk minor mode?

[Kevin Wright]

When I edit rnw files, I frequently find that Emacs becomes confused
about which minor mode should be used.  For example, I might be
editing an R code chunk and delete the chunk-closing '@' sign.  Emacs
will then use LaTeX as the minor mode for the remaining lines of R
code in the chunk.

Is there a command like rescan-buffer-and-identify-minor-modes ?

Does this happen to other people? How can I change my editing
technique to avoid getting into this situation?  Or, maybe my .emacs
config file is causing this...?

I'm running R 2.4.0, current ESS, and Emacs 22 beta (2006-11-05).

Thanks,

Kevin Wright