[ESS] how to stop ESS from switching to R window on its own?

[Peter Kharchenko]

Dear ESS gurus,
  First of all, thanks for a great software - I've been using it for 
years and it's extremely helpful.
  After a certain upgrade ESS started doing something that keeps getting 
in my way, and I want to ask if there's a way to turn this off.
  I typically have two windows (as in window manager windows), with one 
having source code, another running R. When some R code is executing, 
and I am editing the source while that's happening, whenever I type an 
opening paren ESS either splits the source screen and shows the R 
process in there. If the source screen is already split, it shows R 
session in one of the existing panes. I imagine this is some kind of an 
autocomplete attempt. The problem is that the source panes are typically 
there exactly the way I want it, and I don't want ESS switching any views.
  So, is there a way to turn this off (during startup)? I am willing to 
sacrifice autocomplete if that's what it takes ...

thanks in advance,
-peter.